Only an hour ago out why he was absent.A. did the teacher foundB. the teacher foundC. did

问题补充：

Only an hour ago out why he was absent.

A. did the teacher found

B. the teacher found

C. did the teacher find

D. had the teacher found

答案：

A. did the teacher found

B. the teacher found

(答案→)C. did the teacher find

D. had the teacher found

解析：句意，只是在一小时之前，老师才知道了他缺席的原因。当only+状语位于句首时，句子要用部分倒装。所谓部分倒装就是把谓语动词的一部分，即助动词、情态动词、系动词移至主语的前面。因为前面有了助动词或情态动词，所以后边的动词要用原形，故选C。