C.) The amount of mass used up in holding a nucleus together.
Explanation:
The mass defect of a nucleus represents the mass of the energy binding the nucleus. It is the difference between the mass of the nucleus and the sum of the masses of the nucleons of which it is composed.
the answer is a: galaxies. galaxy clusters are groups of galaxies that like to hang out together out there in space. the milky way's own galaxy cluster is called the local group.
