A Woman Inherits a Mutant BRCA1 Allele from Her Mother

A woman inherits a mutant BRCA1 allele from her mother. She has an increased risk of developing breast cancer because

A) every cell in the woman's body has a copy of the mutant BRCA1 allele.
B) she still has one normal allele of the BRCA1 gene that can make up for the loss of function in the mutant allele.
C) some of the cells in her body are already cancerous, meaning that no further mutations are needed for a tumor to form.
D) the normal BRCA1 allele is more likely to mutate than in an individual without a mutant BRCA1 allele.
E) a mutation in her normal BRCA1 allele may lead to cancer, whereas a normal individual would have to acquire two mutations one in each allele) to develop cancer.