. . . . . . does sir ask a question than clever students give an answer.

Correct Answer: D) No sooner

Here's why: This question tests your knowledge of correlative conjunctions.

No sooner...than is a special structure used to show that one thing happens immediately after another.

Let's break down why the other options are incorrect:

A) When: While "when" can introduce a clause, it doesn't create the necessary sense of immediacy like "no sooner...than."

B) Hardly had: "Hardly had" is also a valid construction, but it's paired with "when" (Hardly had...when), not "than." So, the structure is incorrect.

C) As soon as: "As soon as" works but it is often paired with a simple past tense in both clauses to indicate immediacy, but the sentence structure requires No sooner.

D) No sooner: This is the correct option because it completes the correlative pair "no sooner...than." It creates a clear and grammatically correct sentence showing that the students answered almost immediately after the sir asked a question.

Therefore, the complete sentence is: "No sooner does sir ask a question than clever students give an answer."