Question

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．had he realized

Answer 1

C

考查时态及主谓倒装，句意：只有当开始上课时，他才意识到他把书丢在了家里。结合语境可知本句描述的是过去发生的动作，故用过去时态。当only位于句首时，主句用部分倒装，助动词提前。故选C。