Facebook: Why no "Comment" for some posts?

Factual Questions
1

I mostly go to Facebook to see what my friends are posting, but occasionally, I will see a post that I would like to comment on. Sometimes, though, there is no place to put a comment, even though I see other people’s comments.

Sometimes, there is a clickable link “Comment”, but other times there is not.

Why?

2

If your friend A comments on her friend B’s post, then you will be able to see B’s post and A’s comment, but depending on how B has her privacy settings, you wouldn’t be allowed to comment, since you’re not friends with B.

3

^Answered in one.