the teacher was annoyed when he found one third of the students __absent from the lesson.

题目

the teacher was annoyed when he found one third of the students __absent from the lesson.
A have been B were
想问为什么不用A,发现时不应该是已经发生的事情了吗,

答案

时态一致啊亲,主句过去时,所以从句也要用和过去相关的时态