Question

We .......................... be quiet in the library.

• A. mustn't
• B. doesn't have to
• C. doesn't
• D. must

Hint:

Differentiate between 'must' and 'have to' (for obligation) and 'mustn't' (prohibition) and 'don't have to' (lack of obligation). In formal rules and regulations, 'must' is very common.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
This question tests the use of modal verbs to express obligation or necessity.
Step 2: Detailed Explanation:
The sentence expresses a rule or a strong obligation to be quiet in a library.
- mustn't: expresses a prohibition (it is forbidden).
- doesn't have to: expresses a lack of obligation. Also, "doesn't" does not agree with the subject "We".
- doesn't: is not a modal verb and does not fit grammatically.
- must: expresses a strong obligation or necessity.
Given the context of a library, there is a strong rule to be quiet. Therefore, "must" is the most appropriate modal verb.
The complete sentence is: "We must be quiet in the library."
Step 3: Final Answer:
The correct option is (D) because "must" correctly conveys the sense of strong obligation required by the context.