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.