Scientists are convincedthe positive effect of laughterphysical and mental health. A. of;

发布时间：2020-08-17 13:17:51

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
(答案→)C. of; on
D. on;at
解析：be convinced of确认，认识到;the effect on对……的影响。
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