题目

By serving others, a person focuses on someone other than himself or herself, ______ can be very eye-opening and rewarding.    A. who       B. which     C. what       D. that 答案：B 解析: which引导非限制性定语从句,指代整个句子。在非限制性定语从句中,必须用which引导,而不用that引导。who引导定语从句时,其先行词是表示人的名词。what不用于引导定语从句,而用于引导名词性从句。50厘米=50%厘米．______．