. . . . . . . . does sir ask a question than clever students give an answer. A. No sooner B. Hardly had C. When D. As soon as

The correct answer is: As soon as.

The other options are:

• No sooner: This means “immediately after”. It is used to describe two events that happen very close together in time. For example, “No sooner had he arrived than the phone rang.”
• Hardly had: This is similar to “no sooner”, but it is used to describe two events that happen even closer together in time. For example, “Hardly had he sat down when the phone rang.”
• When: This is used to introduce a clause that describes a time when something happens. For example, “When the phone rang, he jumped up.”

In the given sentence, we are looking for a word that describes the relationship between the teacher asking a question and the students giving an answer. The best word for this is “as soon as”, because it indicates that the students give an answer immediately after the teacher asks a question.