Given that A is a non-empty subset of real numbers, if I(A) denotes the set of interior points of A; then I (A) is:-
a) empty. b) singleton. c) a finite set containing more than one element. d) countable but not finite.
I know that the largest open set contained in A is called interior of A. Also a point is said to be interior point of A if we have an open ball of finite radius contained in A.
My trouble is I am not able to figure out the interpretation from the given statement as it is not given anything else beside non empty subset.