Cystic fibrosis is an inherited genetic disorder caused by two copies of a defective recessive gene that causes

A) senility at around age fifty and slow nervous system damage.
B) the buildup of fluid in the lungs, and complications from pneumonia.
C) a form of mental impairment, along with heart defects, and a webbed neck.
D) the inability of the blood to clot properly, resulting in organ damage and easy bruising.