Scientists are convinced the positive effect of laughter physical and mental health.
A. of;at
B. by;in
C. of;on
D. on;at
网友回答
A. of;at
B. by;in
(答案→)C. of;on
D. on;at
解析:convince 意为“使确信,说服”,与介词of连用,意为“使(人)承认或信服”。effect 意为“作用,功效,影响”,与介词on连用,表示“对……有影响”。