What Is the Best Description of the Genetic Contribution to Onset

What is the best description of the genetic contribution to onset of autism?

A) Autism spectrum is caused by a single gene mutation in most,but not all,cases.
B) Exposure to a teratogen can be a cause of autism spectrum in many cases.
C) Known causes of autism spectrum include copy number variants and chromosomal problems.
D) Autism spectrum disorders have a much stronger environmental input than genetic input to expression of the phenotype.