问题
选择题
Scientists are convinced______ the positive effect of laughter______ physical and mental health.
A．of ; at
B．by ; in
C．of ; on
D．on ; at
答案
答案：C
考察介词。Be convinced of 为固定词组，意为对……信服 effect on sth 意为对……的影响 为固定短语 ，所以选择C
句意为，科学家们对笑声对身心健康产生的影响深信不疑。
