Question

Fill in the blank with a suitable modal:
"I can't sleep."
"You ________ drink coffee at night."

• A. must
• B. shouldn't
• C. don't have to
• D. have

Answer 1

Answer: (B)

shouldn't

Answer : B

Modal verbs are auxiliary verbs that are used to express necessity or possibility.

Let's take a look at the usage of the modal verbs in the options:

• must : to express a necessity (in the present or future); to make an assumption that something is true
• shouldn't : It is the contracted form of 'should not'; it is the negative form of the modal verb 'should'
• don't have to : It is the negative form of "have to"; & is used to express that something is not a necessity / obligation; & is used to express absence of an obligation or necessity
• have : It is an ordinary verb, that means to ''possess'' / "own"

Here in the question, we see that the speaker is expressing an advice to NOT drink coffee at night, because coffee has caffeine, which keeps your brain active and delays sleep.

• As it is an advice and NOT a necessity or obligation -- "must" is NOT suitable here.
• "don't have to" coveys that there is no necessity or obligation, it is not used to express an advice, thus it is also NOT suitable here.
• "have" is an ordinary verb and grammatically it does not fit here in the sentence.
• "shouldn't " is appropriate because it is used to convey an advice in the negative sentences, which here is to NOT drink coffee at night.

Therefore from among the options, 'shouldn't' is the most suitable verb to complete the sentence.

Thus, the correct complete sentence is:

"You SHOULDN'T drink coffee at night."