His writing is so confusing that it's difficult to make out he is trying to express.A. w

问题补充：

His writing is so confusing that its difficult to make out he is trying to express.

A. what is it

B. what is it that

C. what is that

D. what it is that

答案：

A. what is it

B. what is it that

C. what is that

(答案→)D. what it is that

解析：D 考察宾语从句和强调句型。空格处引导一个宾语从句，在从句做又包含着what引导的强调句的特殊疑问句，排除AC，what引导的特殊疑问句作为make out的宾语要使用陈述语序。故D正确。