Topic: Sequence of Tense,

Best Answer Explained in Below-:

The phrase "It is high time you—up smoking" requires a specific verb form that aligns with the expression of urgency or necessity inherent in the statement. The correct answer is "b) gave," resulting in the complete phrase "It is high time you gave up smoking."

In English, the expression "it is high time" is often used to indicate that something should have been done already, implying a sense of overdue urgency. When we follow "it is high time," we typically use the past subjunctive form of the verb. This is why "gave" (the past tense of "give") is appropriate instead of "give" (the base form), "have given" (present perfect), or "will give" (future tense).

Using "gave" in this context suggests that the speaker believes it is not just advisable, but necessary for the listener to stop smoking at this point in time—indicating that they should have perhaps already made this change. Therefore, the correct choice encapsulates both the urgency and the implied past necessity of the action.