Understanding Mendelian genetic heredity

When a fruit fly of genotype Mm Nn Oo is mated to another fly of identical genotypes, what proportion of the progeny flies will be MM nn Oo?  (Assume that the three genes are independent)
(a) 1/2
(b) 1/8
(c) 3/8
(d) 1/32
(e) 1/64