Question

what is the most common lethal genetic disorder among caucasians in the united states?
a down syndrome
b hemophilia
c spina bifida
d cystic fibrosis

Explanation:

Cystic fibrosis is a common lethal genetic disorder among Caucasians in the US. Down syndrome is a chromosomal disorder (not typically lethal in the same sense as cystic fibrosis in the context of the question's phrasing). Hemophilia is a bleeding disorder (more about blood - clotting issues rather than being the'most common lethal' as per the question). Spina bifida is a neural tube defect (not the most common lethal genetic disorder among this group).

Answer:

D. Cystic fibrosis