Scientistsareconvinced.

问题详情：

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

A. of; at                       B. by; in                C. of; on               D. on; at

【回答】

解析：选C。句意：科学家们坚信笑对身心健康有积极影响。be convinced of=be completely sure about sth. 坚信，深信，确信；effect常与on连用，表示“对……的影响”。以上两个均属于固定搭配。

知识点：介词

题型：选择题