Complex genetic diseases are different from single-gene diseases because they
a. cause death almost instantly
b. are caused by mutations to multiple genes
c. are more easily passed from one generation to the next
d. cannot be affected by lifestyle choices

I believe the answer is: B. are caused by mutations to multiple genes

Compared to single genetic diseases, Complex genetic disease are less likely to happen because it need both multiple mutation and environmental factors to be developed. Examples of complex genetic disease are Parkinson, Alzheimer, and Autism.