Answer:
C. Incomplete dominance
Step-by-step explanation:
Incomplete dominance is a type of non-mendelian inheritance in which one allele does not completely mask the phenotypic expression of the other allele in a gene, hence, the blending of both alleles give rise to an intermediate third phenotype.
According to this question, there are three options for fur color in mice namely: black, grey and white. This is so because the alleles for black and white coloration exhibits INCOMPLETE DOMINANCE, hence, they produce a third phenotype (grey) that is a blend of both parental phenotypes.