隋朝大运河是哪位皇帝在位时开通的（    ）

我国是一个统一的多民族的国家，维护民族团结是每个公民的义务。下列说法正确的是（  ）

①学习、宣传我国的民族政策                                         ②到少数民族地区旅游，学习少数民族文化

③和少数民族同学开玩笑，嘲笑少数民族同学讲话     ④尊重少数民族的风俗习惯和宗教信仰

A : What's your favourite invention?

B : Of course computers. They are very important in people's life now.       

A: I like computers, too. I think they will be used even more widely in the future.

B: I agree with you.        

A: I usually use my computer for looking up information reading books and playing games;

B: Do you like shopping online?

A : Yes, of course.       

B: That's true. However, sometimes it isn't safe to buy things online.

A: Yes, so we should be careful when shopping online. What do you like to do with your computer?

B:        

A: You must have many net friends.

B: Sure. I have about 10 friends who are from different countries.

A:        

4位同学各自在周六、周日两天中任选一天参加公益活动，则周六、周日都有同学参加公益活动的概率为（　　）