Scientists are convinced _______ the positive effect of laughter _______ physical and mental health....
2022-08-15 07:00:15 196次 黑龙江省哈尔滨市2019-2020学年高二10月月考英语试卷 单项填空 反馈错误 加入收藏 正确率 : 100%
题目内容：
Scientists are convinced _______ the positive effect of laughter _______ physical and mental health.
A.in; on B.of; on C.on; at D.in; at
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