Answer
(d) None of the other options are true for the center of mass of an object.
Work Step by Step
Let us consider some examples:
1. An irregularly shaped flat board - the center of mass lies somewhere off its center.
2. A regular triangle board with three balls at each corner, one bigger than the others - the center of mass lies somewhere between the three.
3. A ring - the center of mass lies outside the body.
So, none of the options (a), (b) or (c) is true.
