Correct option is D
Solution:
If there are N fermions and M degenerate states of each energy level for the ground state of the system (not the lowest energy level), all levels with degeneracy will be filled. The uppermost level will have R fermions to be filled in M degenerate levels, and that will be filled in "M choose R" ways, denoted as MCR. That is the degeneracy of the ground state.


