imagine后面引导的是宾语从句.这个宾语从句把原本的陈述句改成了感叹句,即：原来的句子：I had great difficulty finding his address.改为感叹句：What great difficulty I had finding his address.所以答案还是C....引导词是what还是what great difficulty引导词应该是that，但省略了。而且因为宾语从句改成了感叹句用what来引导，所以that不出现。