Based on this information, what is this snail's phenotype for the shell banding trait?

 - a banded shell
 - an unbanded shell
The Cepaea snail's genotype for the shell banding gene is bb. The Cepaea snail's genotype of bb has only b alleles. The b allele is for an unbanded shell. So, the Cepaea snail's phenotype for the shell banding trait must be an unbanded shell.
To check this answer, consider whether the Cepaea snail's alleles are dominant or recessive. The allele for a banded shell (B) is dominant over the allele for an unbanded shell (b). This means B is a dominant allele, and b is a recessive allele.
The Cepaea snail's genotype of bb has only recessive alleles. An organism with only recessive alleles for a gene will have the recessive allele's version of the trait. So, the Cepaea snail's phenotype for the shell banding trait must be an unbanded shell.