A 40-Year-Old Woman Is Concerned for the Health of Her

A 40-year-old woman is concerned for the health of her child because her own father died of Huntington's disease.The consultand currently has no signs of Huntington's disease himself.If we assume the age-dependent penetrance of Huntington's disease is 20% at age 40,what is the prior probability that the child will have inherited the disease?

A) 1/9
B) 2/9
C) 1/4
D) 1/3
E) 1/2