（）the experiment that he gave up.ASo much trouble did he have doing 选ACSo much trouble did he have to do为什么?
问题描述：
（）the experiment that he gave up.
ASo much trouble did he have doing 选A
CSo much trouble did he have to do
为什么?
答
把句子的顺序调整过来就是
He had so much trouble doing the experiment that he gave up.
句子的结构以及运用的短语就很明显了.
have trouble in doing sth.做某事有困难或很麻烦
其中in可以省略.