His writing is so confusing that it's difficult to make out it is he is trying to expres

问题补充：

His writing is so confusing that its difficult to make out it is he is trying to express.(·安徽)

A. that

B. how

C. who

D. what

答案：

A. that

B. how

C. who

(答案→)D. what

解析：句意：他的书写如此令人困惑，以至于难以辨认他在试图表达什么。分析句子结构可知，定语从句he is trying to express后缺少宾语，因此用what。