问题
选择题
Scientists are convinced ________the positive effect of laughter________ physical and mental health.
A．of; at
B．of; on
C．by; in
D．on; at
答案
答案：B
考查介词辨析。be convinced of 相信… ; “对…有影响” 应用介词on。句意：科学家们相信笑声对身体和精神健康有积极地影响。故B正确。