(2013·日照一模)—What has made John look like lacking sleep?
— he had to prepare for the ing exam and stayed up last night.
A. For
B. Because
C. That
D. What
网友回答
A. For
B. Because
(答案→)C. That
D. What
解析：选C 考查名词性从句。分析句子结构可知，答语是回答上面句子中的主语“What”的，故此句是一个主语从句，缺少引导词，而引导词在从句中不充当成分，故用“That”。