In cats, the Dense pigment gene, D/d, codes for melanophilin, a protein involved in the transportation and deposition of pigment into a growing hair. A separate gene, M/m, is responsible for the production of the pigment, with M_ producing black pigment and mm producing brown. When a cat has two recessive d alleles, its fur is a light gray color regardless of which alleles of M/m are present.

Required:
State the phenotype and frequency for each of the following outcomes of a dihybrid cross:

a. M_D_
b. M__dd
c. mmD
d. mmdd