题目内容：

求大师详解：only when he had handed in his exam paper, __ he had made several grammatical mistakes. 用这个had he relized 行吗?

优质解答

did he realize
only在从句句首,主句用倒装 结构
而前面俩个动作hand in和make mistakes都是发生在realize之前,所以用过去的过去,而realize只要用一般过去就好