He ________ have been nervous because he didn't go straight in. A. ought to B. must C. should D

He ________ have been nervous because he didn't go straight in. A. ought to B. must C. should D. had to

The sentence requires a modal verb expressing a past deduction based on evidence ("he didn't go straight in"). "Must have" is used to conclude a past situation with certainty, making it the right choice here.

Answer: B. must

The structure "must have + past participle" indicates a logical inference about something that likely happened in the past. In this case, the observation "he didn't go straight in" leads to the conclusion that nervousness was the reason, making "must have been" the appropriate modal phrase. Other options fail: "ought to have" and "should have" express unfulfilled obligation, while "had to" indicates past necessity—none convey the deductive meaning needed here.