正确答案，是keeps,出乎意料吧，怎么解释？

【 在 valah 的大作中提到: 】
: 第37空
: “What do you want to be when you grow up?"There are different_ 36_( answer ) to this question.
: Some people want to be doctors to save lives. Some people want to be famous singers. I hope that I will be an expert_ 37_(keep) the earth clean.
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