What Is/are the Central Question(s) in the Part of Philosophy

Multiple Choice

What is/are the central question(s) in the part of philosophy of mind often called the "problem of other minds"?

A) Do other people (and things like robots or fish) have mental states?
B) Are other people's (things') mental states similar to yours?
C) How can we know whether other people (things) have mental states and whether they are similar to yours?
D) All of the above