Scientists are convinced the positive effect of laughter physical and mental health.A. of,onB. by,in

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【题目】Scientists are convinced ______ the positive effect of laughter ______ physical and mental health.

A. of；onB. by；in C. of；at D. on；at

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【答案】A

【解析】

试题分析：考查介词搭配。短语be convinced of相信...；have an effect on对...有影响；句意：科学家们相信笑对身体和精神的积极影响。故A正确。