I know the answer is c) 4, but I don't understand why. Can someone please give a thorough explanation going line by line please.

7.A recursive function is defined as int mystery (int k) if (k 1) return 0; else return (1 mystery (k/2)) i What value is returned by the call mystery (16)? a) 0 b) 4 e) No value is returned because the call causes an infinite recursion