【题目】Scientists are convinced ______ the positive effect of laughter ______ physical and mental health.
A. of; at B. by; in C. of; on D. on; at
在线课程【答案】C
【解析】
试题分析：考查介词。本句第一空考查短语：be convinced of，意为确信、相信。第二空考查短语：the effects on。故选择C，句意为：科学家相信笑对于人的身心健康有好处。