Aggregation Studies Concerning the Genetics of Stuttering Have Shown That

Aggregation studies concerning the genetics of stuttering have shown that the inheritance of stuttering:

A) fits well with a single major locus model (one or several main genes being responsible)
B) is more through affected mothers than affected fathers
C) is equally accounted for by both genetics and environmental factors
D) fits best with polygenic model (many genes but no environmental factors) .