Context: This passage describes the sickle-cell disease trait in humans:

In a group of humans, some individuals have sickle-cell disease and others do not. In this group, the gene for the sickle-cell disease trait has two alleles. The allele for not having sickle-cell disease (A) is dominant over the allele for having sickle-cell disease (a).
Stacy is a human from this group. Stacy has the homozygous genotype aa for the sickle-cell disease gene.
Based on this information, what is Stacy's phenotype for the sickle-cell disease trait?
A. not having sickle-cell disease
B. having sickle-cell disease
Identify the correct choice from the options below and respond with the letter of the correct option.

B