Answer:
D. gene expression due to the differences in abiotic conditions
Step-by-step explanation:
Phenotype is the morphological expression of genotype. Besides the genes, a phenotype is also affected by environmental conditions such as water, light, food availability etc. Since the rabbit produces specific fur color in winter season only, the expression of the gene coding for fur color must be affected by environmental conditions present in winter season giving it a different phenotype from that of summer season.