BRCA1 and BRCA2 are considered to be tumor-suppressor genes ...

[aero]

BRCA1 and BRCA2 are considered to be tumor-suppressor genes because
A) they prevent infection by retroviruses that cause cancer.
B) their normal products participate in repair of DNA damage.
C) the mutant forms of either one of these promote breast cancer.
D) the normal genes make estrogen receptors.
E) they block penetration of breast cells by chemical carcinogens.

[Hawke]

I'd go with B. It makes sense.

[aero]

Thanks Hawke