问题补充：
some students are not aware of is difficult life can be if they are not devoted to study.
A. That; how
B. Which; what
C. What; what
D. What; how
答案：
A. That; how
B. Which; what
C. What; what
(答案→)D. What; how
解析：D句意：一些学生没有意识到的是如果他们不专心学习，生活可能会是多么的难。“some students are not aware of”为主语从句，该从句缺少宾语，表示“事物”且语境中并无选择含义，故用what引导；“difficult life can be”为表语从句，其中life为主语，设空处后为形容词，故用how引导。本题易误选C项，考生误以为第二空后的difficult life为名词，故用what引导，但是如果那样的话“difficult life can be”便没了主语，也就不能成为一个从句，第二空如果填what，应改为：what difficult life it can be。
