The correct answer is B.
Black, gray, or white fur.
This is because the gray cat has one allele for black fur and one allele for white fur, while the white cat has two alleles for white fur. When they reproduce, the kittens can inherit either the black allele or the white allele from the gray cat, and they will always inherit the white allele from the white cat. Therefore, the kittens can have black, gray, or white fur, exhibiting all three phenotypes.