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
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:C