Children won't put on weight so easily if they ________ to eat more fruit and vegetables．
A.persuadeB.were persuadedC.will persuadeD.are persuaded在线课程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。