Context: In a group of Labrador retrievers, some individuals have black fur and others have brown fur. In this group, the gene for the fur color trait has two alleles. The allele for brown fur (f) is recessive to the allele for black fur (F).
Rolf is a Labrador retriever from this group. Rolf has the homozygous genotype ff for the fur color gene.
Based on this information, what is Rolf's phenotype for the fur color trait?
A. brown fur
B. black fur
Determine the correct option from the provided choices and reply with its corresponding letter.

A