Remember that f(a) is the same thing as y just about. So the y value is -2. That's the flat part of the graph about.
You need an x value that is along the flat part of the graph.
The flat part goes from x = - 1 to x = 0
You need a value between 0 and - 1. The only value there that does that is B.
I don't know why the answer was given to you as A. It is not correct. Sometimes questions are like that. There's just an error in them. Appeal it with your teacher.
B <<<<<< answer.