问题补充:
Only when class began that he had left his book at home.
A. will he realize
B. he did realize
C. did he realize
D. should he realize
答案:
A. will he realize
B. he did realize
(答案→)C. did he realize
D. should he realize
解析:考查倒装结构。当only等词谓语句首时,主句采用部分倒装,句意:直到上课开始时,他才意识到他已经把书丢在家里面了。结合语境可知此处描述的是过去的动作,故用过去时态,助动词用did,故选C。