Ну вроде того:
3.
1) Usually I use only v k. c o m, because it was the first one that I've known and I have more friends there.
2) The most popular social networks in my country are v k. c o m, m a i l. r u and facebook.
3) Usually people exchange the information about their life, events, news etc.
4) I think they are popular because they are old and have a lot of additional features.
5) In my opinion social network sites bring only two dangers, that I can describe like dingy acquaintances and spending too much time sitting in front of computer.