计划将排球、篮球、乒乓球3个项目的比赛安排在4个不同的体育馆举办，每个项目的比赛只能安排在一个体育馆进行，则在同一个体育馆比赛的项目不超过2个的安排方案共有（    ）

在实验设计中，下列选项中不能作为一组对照的是（　　）

完形填空

Most American families are smaller than those in other countries. They have one or two （1）________ and one or two children each.

Children in the US will（2）________ their parents' house when they grow up. They usually live（3）________ their parents because of work. They often（4）________ to their parents or telephone them. And they often go to visit their parents when they are（5）________ vacation.

Parents usually let their children choose their（6）________ jobs. Americans think it's （7）________ for young people to decide their future by themselves.

Parents also （8）________ their children to do some housework at home. And in many families, children are paid for （9）________ housework. Parents think it can help them learn（10）________ to make money for their own use.

下列各句中，划线的成语使用不恰当的一项是（    ）