Answer:
the point about which an unconstrained rotation occurs
the mass-weighted center of the object
Step-by-step explanation:
The center of mass of an object can be described to be a a position that is defined relative to the object
The center of mass is the average position of every parts of the object. At this point we can assume that all of the mass of this object is concentrated
When weighted according to their masses, the center of mass is the average position of all the parts of the object. While other points in this object are rotating around it, the center of mass would not rotate (fixed).
So the correct options are:
1. the point about which an unconstrained rotation occurs
2. the mass-weighted center of the object