问题补充：
There came a point in his life he had to think about seriously about his future.
A. what
B. that
C. when
D. which
答案：
A. what
B. that
(答案→)C. when
D. which
解析：句意：他的生活到了他不得不认真思考关于他的未来的一个时刻。What代词，引导名词性从句；which和that是关系代词，引导定语从句，并作主语，宾语，表语；when关系副词，引导定语从句，可作时间状语。空格前的point “时刻”是定语从句的先行词，故排除A项。空格后的定语从句不缺少主语和宾语，故排除B项和D项。因此选C。
