Modal Verbs

Why A (must) is correct:
"Must" expresses a strong obligation or rule—libraries require silence, so this is the right choice.

Why the others are wrong:
- B (may) suggests permission ("you are allowed to"), not obligation
- C (might) expresses possibility ("perhaps you will"), not a requirement
- D (could) shows ability ("you are able to"), not a rule or duty

Why A (May) is correct:
"May" is the polite, formal way to ask permission. It's the standard choice for requesting to do something in proper English.

Why the others are wrong:
- B (Might): This suggests possibility or uncertainty about a hypothetical situation, not a polite request for permission.
- C (Will): This is a statement or prediction, not a request—it's too direct and demanding.
- D (Could): While "could" can ask permission informally, "may" is more formal and appropriate in standard English.

Why A (Could) is correct:
"Could" is the past tense of "can," which expresses ability in the past. The sentence describes something you were able to do at age five, so you need the past tense form.

Why the others are wrong:
- B (May) – This expresses permission or possibility, not ability. It doesn't fit the meaning.
- C (Might) – This expresses uncertainty or possibility, not a definite past ability.
- D (Can) – This is present tense, but the sentence is about the past (age five). You need past tense.

Why A (Can) is correct:
"Can" is the natural choice for making a polite request about someone's ability to do something for you. It asks if the person has the ability or permission to change your room.

Why the others are wrong:
- B (Should) - This asks for advice/obligation ("ought to"), not a request. It would mean "Is it a good idea for you to change my room?"
- C (Might) - This expresses possibility, not a request. It's too uncertain for asking someone to do something.
- D (Could) - While grammatically acceptable and polite, "can" is more direct and natural for this request in most contexts.

Correct answer: A (can)

"Can" works here because it means "are able to" or "have the ability to" ask her again—a simple, grammatically correct statement.

Why the others are wrong:

• B (must to): Incorrect grammar. "Must" is already a modal verb and doesn't take "to" after it. It would be just "must ask."
• C (might): While grammatically possible, "might" suggests uncertainty or possibility ("we possibly could ask"), which doesn't fit the straightforward meaning of the sentence.
• D (could): Also grammatically correct, but "could" implies past ability or a hypothetical situation, whereas "can" is more direct and natural for this simple statement.

Correct Answer: A. couldn't

This sentence describes a past inability—he didn't have the ability to dance before lessons. "Couldn't" is the past tense of "can't" and correctly shows he lacked this ability in the past.

Why the others are wrong:
- B. could – This means he *had* the ability, which contradicts the logic (he couldn't dance *until* lessons helped him)
- C. can – This is present tense, but the sentence refers to the past ("until he took lessons")
- D. might – This suggests possibility, not inability; it doesn't fit the meaning of the sentence

Could is correct because it's the most polite way to make a request in English.

• Could = polite request (best choice for asking someone to do something)
• May = asking for permission (you'd use this if asking "May I open the window?" but not for requesting someone else to do it)
• Might = expresses possibility, not used for requests
• Can = less polite; it questions ability rather than making a courteous request

Why C is correct:
"Must" expresses necessity or obligation—cleaning clothes is something you have to do to maintain hygiene and have clean things to wear.

Why the others don't work:
- A (will) – This is future tense, not about obligation. It describes what you'll do, not what you need to do.
- B (should) – This suggests advice or recommendation, but cleaning clothes isn't optional advice; it's a genuine need.
- D (could) – This means you *have the ability* to do something, but doesn't capture the requirement that you actually *must* do it.

Why A (must) is correct:
"Must" expresses certainty or a strong logical conclusion—the speaker is confident that this is the main entrance based on evidence.

Why the others are wrong:
- B (can) means "is able to" or "is possible," but doesn't show certainty
- C (may) suggests permission or weak possibility, not confidence
- D (might) also expresses possibility or uncertainty, similar to "may"

When making a definite statement about what something is, you need the certainty that "must" provides.

A. able ✓

After a negative statement with "wasn't," you need an adjective to complete the phrase. "Wasn't able to" is the correct structure meaning "didn't have the capacity to."

Why the others are wrong:
- B. could – This is a verb, not an adjective. You can't say "wasn't could"; the structure doesn't work grammatically.
- C. can – Same problem as "could"—it's a verb, not an adjective. The base form doesn't fit here either.
- D. may – Also a verb. Plus, "may" expresses permission or possibility, not capability or capacity.

• A. able ✓ Correct. "Haven't been able to" is the proper past participle form needed after the auxiliary verb "have." It correctly describes an ongoing inability over the past year.

• B. can ✗ Wrong. "Can" is a modal verb that doesn't work with "have been." You can't say "have been can."

• C. could ✗ Wrong. "Could" is also a modal verb and doesn't pair with "have been" the same way. "Haven't been could" is grammatically incorrect.

• D. may ✗ Wrong. "May" expresses permission or possibility, not inability. It also doesn't work with "have been" in this structure.

A. able ✓

After "will be," you need an adjective to complete the future continuous structure "will be + adjective." "Able" is an adjective that describes his state or condition.

Why the others are wrong:
- B. can – This is a modal verb, not an adjective. You can't use two modals together ("will can").
- C. could – Also a modal verb with the same problem as B.
- D. may – Also a modal verb; same issue.

Correct answer: A. able

The sentence needs an adjective to complete "were not _____ to get," and "able" is the only adjective among the choices. "Able" means having the power or skill to do something, which fits perfectly here.

Why the others are wrong:
- B. can – This is a modal verb, not an adjective; you'd say "cannot" as one word, not "were not can"
- C. could – Also a modal verb; grammatically doesn't work with "were not"
- D. may – A modal verb for permission/possibility; doesn't fit the meaning or grammar here

A. Shouldn't ✓
This is correct because "shouldn't" expresses advice or recommendation—you're warning someone that eating candy is unwise for their dental health.

B. Would
Wrong—this is just a conditional statement ("you would eat") with no meaning here; it doesn't give advice.

C. Mustn't
Wrong—"mustn't" means a strict prohibition or rule you absolutely cannot break. Eating candy isn't forbidden; it's just not recommended.

D. Might not
Wrong—this suggests possibility ("maybe you won't eat candy"), not advice. It's too weak and doesn't convey that it's a bad idea.

A. carefully ✓
When something is important, you need to pay close attention to details and understand it well. "Carefully" means paying attention and doing something thoroughly—exactly what you need for an important lecture.

B. quickly ✗
Listening fast doesn't help you understand better. In fact, rushing through an important lecture could make you miss key information.

C. loudly ✗
"Loudly" describes *how loud* you listen, not *how well* you listen. It doesn't relate to understanding the content.

D. eagerly ✗
While being eager (enthusiastic) is nice, it doesn't guarantee you'll actually understand the material. You could be eager but careless.

A. need ✓

This sentence requires a verb that means "require" or "have a necessity for." "Need" is the right verb here—you require new glasses because yours broke.

Why the others are wrong:
- B. will — This is a modal verb for future tense, not a main verb expressing necessity
- C. drink — This verb doesn't make sense in context; you don't drink glasses
- D. must — While "must" can express necessity, it's a modal verb that requires another verb after it (like "I must get new glasses"), so it doesn't fit this sentence structure

Correct answer: A. don't have to

This means wearing a tie is *not required*—it's optional. Since the event is casual, there's no obligation to wear one.

Why the others are wrong:
- B. may — Suggests permission/possibility, but doesn't capture that it's *not necessary*
- C. should — Implies recommendation or obligation, opposite of what a casual event means
- D. must — Means requirement/obligation, which contradicts the casual nature of the event

A. needed ✓

The sentence needs a past tense verb to match "was" (past tense). "Needed" correctly shows something you wanted to know in the past.

Why the others don't work:
- B. must – wrong tense; "must" is present/future, but "was" tells us this happened in the past
- C. will – wrong tense; "will" is future, but we need past
- D. needs – wrong tense; "needs" is present, but the sentence is about the past

Why A is correct:
"Must not" expresses a strong prohibition or rule—speaking during an exam is forbidden.

Why the others are wrong:
- B (might not): Suggests it's possible or uncertain they won't speak, not a clear rule
- C (don't have): Incomplete phrase; "don't have to" would mean it's optional, not forbidden
- D (could): Means it's possible or permitted to speak, the opposite of what exams require

Can is correct because it asks for permission—the most natural way to request leaving early from work or school.

• Might: Suggests possibility but doesn't ask permission properly ("Might I leave?" is outdated/formal)
• Will: States a fact or intention, not a request ("I will leave early" sounds like announcing, not asking)
• Must: Expresses necessity or obligation, not a polite request ("Must I leave?" doesn't make sense in this context)

Correct answer: Can't
• "Can't" expresses a logical deduction—since her car is missing, it's impossible she's at home. This fits the situation perfectly.

Why the others are wrong:
• Must – This means she definitely IS at home, which contradicts the evidence (no car).
• May – This suggests possibility, but we have clear evidence to make a definite conclusion, not just a guess.
• Will – This is a future tense prediction, not a logical deduction about the present situation.

Correct answer: might not

"Might not" correctly shows that going to the party is uncertain if it rains—it's a possibility, not a definite decision. Rain creates doubt about whether you'll attend.

Why the others are wrong:
- Must not = a strict prohibition/rule (someone forbids you). Rain doesn't forbid attendance; it just makes it uncertain.
- Can't = impossible. Rain doesn't make going impossible, just less likely.
- Could = is possible, but doesn't express the negative uncertainty. "Could go" suggests you *might* go, not that you *might not*.

Correct Answer: might
- "Might" expresses a past possibility that didn't happen—you thought there was a chance your phone was lost, but it wasn't. This fits perfectly with "I thought it _____ have been lost."

Why the others are wrong:
- May: While similar to "might," "may" is less natural for expressing past hypothetical situations; "might have" is the standard form for this meaning.
- Can: "Can't have been" works for past impossibility ("it couldn't have been lost"), but "can have been" doesn't properly express the meaning of a possible past event.
- Could: "Could have been" can work for past possibility, but in American English, "might have" is more commonly used in this context; "could have" leans more toward ability or capability.

Must is correct because it expresses a necessary obligation or requirement—he is not allowed to play until homework is done.

• Can means ability, not obligation ("he is able to finish")
• Could means possibility or past ability, not a current requirement
• Might suggests uncertainty or possibility, not a firm rule

The sentence describes a rule or condition that must be met, so "must" is the only option that fits.

Why A (May) is correct:
"May" is the most polite and formal way to ask permission. It directly requests whether something is allowed.

Why the others are wrong:
- B (Might): This expresses possibility or uncertainty ("It might rain"), not a request for permission.
- C (Do): This doesn't make sense in this context and doesn't ask for permission ("Do I borrow...?" is grammatically incorrect here).
- D (Could): While "could" can ask permission, it's less formal and polite than "may." "May" is the better choice when making a courteous request.

Correct answer: A (may)

"May" is correct because it expresses permission—you are allowed to ask your teacher for help during the exam. This is what typically happens in real exam situations.

Why the others are wrong:

• B (must) – This means you are required to ask, which isn't the point; asking is optional, not mandatory.
• C (may not) – This means you are forbidden to ask, which contradicts the reality that asking for help is permitted during exams.
• D (might) – While "might" can express possibility, it suggests uncertainty about whether help is available, rather than clearly stating that you have permission to ask.

Correct: A. can't
This sentence contrasts two ideas: you don't have the money, BUT you need it anyway. "Can't" shows this conflict—you lack the ability to afford it, yet you must buy it for work reasons.

Why the others are wrong:
- B. can – This contradicts the contrast; if you could afford it, there'd be no conflict.
- C. might – This suggests possibility, but the sentence needs certainty about your financial situation.
- D. might not – This is too uncertain; the sentence structure demands a definite statement about what you can/cannot do.

Can is correct because it's the most natural and direct way to ask for permission or request a favor in everyday conversation.

• May is too formal for casual hotel requests; it's more common in formal or official settings.
• Might suggests uncertainty or possibility rather than making a clear request—it sounds awkward here.
• Could is polite but less direct than "Can" for simple service requests like this one.

Why A (can) is correct:
"Can" means "are able to," which fits grammatically and logically. You're saying you're able to ask her again.

Why the others are wrong:

• B (may) - means "are permitted to" or "possibly will." While grammatically possible, it changes the meaning to asking permission rather than expressing ability.

• C (might) - means "possibly could." This works grammatically but is weaker and more uncertain than the direct statement of ability that "can" provides.

• D (have) - doesn't work here. "Have ask" is incomplete; you'd need "have to ask" for it to be grammatical, which changes the meaning entirely.

Why "may" is correct:
"May" expresses possibility—going to the gym *possibly* will help relieve stress, which is a reasonable suggestion. It's appropriately uncertain because the outcome isn't guaranteed.

Why the others are wrong:
- Might: While "might" also means possibility, "may" is the more natural choice for suggestions or polite statements about what could happen.
- May not: This means it probably *won't* help, which contradicts the encouraging tone of the suggestion.
- Must: This is too strong—it claims the gym *definitely will* help, which is an unfounded certainty.