问题
选择题
His writing is so confusing that it's difficult to make out ________ it is he is trying to express.(2011·安徽)
A．that
B．how
C．who
D．what
答案
答案：D
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。