Question

______ not swim in the river as the current is very fast.

• A. need
• B. must
• C. dare
• D. would

Hint:

The negative form \textbf{must not (mustn't)} is used to express prohibition or strong warning, such as in safety instructions.

Answer 1

The Correct Option is B

Step 1: Understanding the meaning of the sentence.
The sentence gives a warning or strong advice not to swim in the river because the current is very fast. Therefore, the correct modal verb should express prohibition or strong necessity.
Step 2: Understanding modal verbs.
Modal verbs such as need, must, dare, and would express different meanings in English grammar. Among them, must is commonly used to express strong obligation or prohibition when used in the negative form.
Step 3: Forming the correct sentence.
Using the correct modal verb, the sentence becomes: You must not swim in the river as the current is very fast. This clearly indicates a strong warning or prohibition.
Step 4: Analysis of options.

• (A) need: Incorrect. Need not means there is no necessity, which does not fit the warning given in the sentence.
• (B) must: Correct. Must not expresses prohibition or strong advice against doing something.
• (C) dare: Incorrect. Dare not expresses lack of courage rather than prohibition.
• (D) would: Incorrect. Would not is generally used for habitual actions in the past or conditional situations.

Step 5: Conclusion.
Since the sentence expresses a strong warning due to danger, the correct modal verb is must.
Final Answer: must.