Complete the sentence with the correct form of the verb given in the brackets:I was teaching English when she _____ the classroom. (enter)

The correct answer is A. entered.

The sentence is in the past simple tense, so the verb “enter” must also be in the past simple tense. The other options are not in the past simple tense.

• Option B, had entered, is in the past perfect tense. The past perfect tense is used to talk about something that happened before another event in the past. In this sentence, there is no other event in the past that the teacher’s entering the classroom happened before.
• Option C, will have entered, is in the future perfect tense. The future perfect tense is used to talk about something that will happen before another event in the future. In this sentence, there is no other event in the future that the teacher’s entering the classroom will happen before.
• Option D, has entered, is in the present perfect tense. The present perfect tense is used to talk about something that happened at an unspecified time in the past or that is still happening now. In this sentence, the teacher’s entering the classroom happened at a specific time in the past, so the present perfect tense is not appropriate.