Obviously the left one.

In physics, the center of mass of a distribution of mass in space is the unique point at any given time where the weighted relative position of the distributed mass sums to zero. For a rigid body containing its center of mass, this is the point to which a force may be applied to cause a linear acceleration without an angular acceleration.

If they wanted this to be an actual, debatable question, they shouldn't have used 'center of mass', as the term has a specific definition and the question has a correct answer; it's not open to interpretation, like "How would a horse wear pants?" or similar questions.