Children won't put on weight so easily if they ________ to eat more fruit and vegetables．

A.persuade

B.were persuaded

C.will persuade

D.are persuaded

答案及解析： D

解析：

根据句意“如果孩子们被说服多吃水果和蔬菜，那他们就不会增加体重了”可知应用一般现在时的被动语态，答案为D项。