问题

Scientists are convinced_the positiveeffect of laughter_physical and mental health.

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

正确答案是：

同类题型

I’m afraid I can’t help you ________ your problem.—Thank you all the same. I can ask Simon _______ help.

_____ is good for both young and old people. [ ]

Mary had_______much work to do that she stayed at her office all day long.

Lucy,doyou go to the park—Three times a week.

下列文学文化常识，表述有误的一项是