Scientists are convinced the positive effect of laughter physical and mental health.A. of;

发布时间：2020-08-15 00:39:59

Scientists are convinced    the positive effect of laughter   physical and mental health.
A. of; at
B. by; in
C. of; on
D. on; at

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A. of; at
B. by; in
C. of; on
D. on; at
解析：be convinced of 确信。effect on……，有关于------方面的影响。
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