In the Section "Investigating Life: Does Natural Selection Maintain Cystic

In the section "Investigating Life: Does Natural Selection Maintain Cystic Fibrosis?",one in 25 caucasians is a carrier for the defective CFTR gene,making it the most common genetic disease in this population.Why are the frequency of defects in CFTR so common in caucasians?

A) Carriers with one copy of the defective CFTR gene have decreased resistance to cholera compared to those with no defective copies.
B) These individuals were exposed to cholera,causing mutations in their CFTR gene that can then be passed on to their children.
C) Carriers will be more likely to have children who develop cystic fibrosis.
D) Carriers with one copy of the defective CFTR gene have increased resistance to cholera compared to those with no defective copies.
E) Only carriers would be able to survive exposure to cholera.