Dr. Danah Boyd mentions that having a friends only network is virtually impossible because in social media you have the change to know all people you would never have the chance to know about in real life. Besides Teenagers don't see privacy as a problem towards others, they feel more invaded for their peers and loved ones.
Being this said the correct answer is People will always feel pressure to keep adding "friends".
The other options are not correct because it is said that teen don't see privacy with the same eyes adult will do so they don't always value it, not everyone in the world will eventually be your friend because we have a selection for people according to our filters when we use the setting option, and Parents are always interested in what their kids might be doing on this networks.