题目

It’s probably a good idea for parents to allow teenagers to ________in groups after school in the afternoon because this helps them keep healthy as well as become good friends.A.study B.design C.exercise 答案：【答案】C【解析】句意：家长允许青少年下午放学后参加团体锻炼可能是一个好主意，因为这能帮助他们保持健康，而且也可以使他们成为好朋友。考查动词辨析。study学习；design设计；exercise锻炼。because引导原因状语从句，根据从句this helps them keep healthy as well as become good friends，可知，团体锻炼既可9．函数y=log${\;}_{\frac{1}{3}}$（-3+4x-x2）的单调递增区间是（　　）A．（-∞，2）B．（2，+∞）C．（1，2）D．（2，3）