кортко ответить на вопросы Answer the guestions:
What different kinds of social network sites are there?
Why are some companies creating their own social networks?
Can you restrict some people’s ability to visit your network page?

1) There are some types of social networks. First, Social connection sites, for example, My Space, Facebook, twitter, etc. Second, Multimedia sharing sites such as Youtube, etc. Next, I'd mention professional sites (Linkedln). Finally,  I'd draw your attention to informational sites, e.g. Do-It-Yourself community

2)Lots of companies are interested in better advertising and promotion of their products

3) I can block some IPs or even countries. What is more, I can use a hosting company which provides blocking as part of their built-in controls

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