They . . . . . . . . at school yesterday. A. did B. were C. had D. what

The correct answer is: B. were

The verb “were” is the past tense of the verb “to be.” It is used to describe a state of being or to express a location. In this case, the sentence is asking what the people were doing at school yesterday. The answer is that they were at school.

The other options are incorrect because they do not make sense in the context of the sentence. The verb “did” is used to describe an action. The verb “had” is used to describe possession or experience. The verb “what” is a question word.

Here are some examples of how the verb “were” can be used:

• I was at school yesterday.
• They were happy.
• The cat was on the mat.

I hope this helps!