The Internet has become part of young people’s life. _1. _______ report shows that 38% of students often use the Internet. Most of them get _2.________ (use) information on the Internet _3._______ use the Internet to help with their studies. But many students don’t use it _4.________ a good way. Some play games too much, and some visit websites __5.__________ shouldn’t look at. So bad things may happen __6._________ students spend too much time on the Internet.

__7._______ is important for students to use the Internet properly. Now we have a textbook, __8._______ uses many examples to teach students some good ways to use the Internet. It gives useful __9._______(advise).

Some students also make friends on the Internet. But if you want to have a face-to-face _10.__ ______ (meet) with your online friends, please let your parents know and meet in a proper place.

下列判断正确的是（）。

A.AsH₃、MgO都是共价化合物

B.As₃、HCl都是共价化合物

C.CaF₂、AsH₃都是离子型化合物

D.CaF₂、SO₂都是共价化合物