The Parents of a Child Diagnosed with Cystic Fibrosis Ask

The parents of a child diagnosed with cystic fibrosis ask the nurse how their child developed the disease. Which of the following should the nurse explain to these parents?

A) Cystic fibrosis is a disease that has an extra chromosome.
B) Cystic fibrosis is an X-linked disorder.
C) Cystic fibrosis is passed on by a defective gene from both parents.
D) Cystic fibrosis is passed on by one defective gene from one parent.