By serving others, a person focuses on someone other than himself or herself, ___________ can be very eye-opening and rewarding.A.whoB.whichC.whatD.that
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B解析思路分析：空缺处引导一个定语从句，且在从句中作主语，代替整个主句内容，故用which。that不可引导非限制性定语从句。
【点评】此题考查定语从句的引导词，难度偏易。只要判断出空缺处所起作用便可迎刃而解。