Final answer:
Epistasis is an interaction between genes in which one gene masks or modifies the expression of another gene. In the example of pigmentation in mice, the C gene is epistatic to the A gene.
Step-by-step explanation:
Epistasis is an interaction between genes in which one gene masks or modifies the expression of another gene. In the example of pigmentation in mice, the C gene is epistatic to the A gene. The presence of the recessive c allele at the C locus negates pigment production, resulting in an albino phenotype regardless of the allele present at the A locus. Therefore, option B is correct, laci is epistatic to lacZ.