Answer:
Bb
Step-by-step explanation:
Heterozygous means different alleles. Since for color, there are, in this situation, 2 alleles, B and b, let's say. B being black dominant, and b being black recessive, or white, let's say. For the rabbit to be black, it needs only one dominant allele. Since the rabbit is heterozygous, the genotype is Bb. I hope I helped, and sorry if this was confusing!