求教一道英语单选

题目

求教一道英语单选
By serving others,a person focuses on someone other than himself or herself,___can be very eye-opening and rewarding.
横线上是填who 还是 which?
试题答案给的是which 我们老师认为是who 他也拿不准 = =

答案

which
which指的是“帮助他人,从仅仅关注自己变成关注他人By serving others,a person focuses on someone other than himself or herself”这件事.