How Would You Describe the Social Networking Site YouTube

How would you describe the social networking site YouTube?

A) YouTube is a microblog that lets users post photos and then organize them into albums,add tags to categorize them,and invite comments.
B) YouTube is a media-sharing network that lets users display and view videos and then post comments.
C) YouTube is a discussion forum network that lets users have conversations on any topic.
D) YouTube is a social curation site that lets users share and save links to websites on selected news topics to target the most relevant,useful,and high-quality information.