Newborns of Mothers Who Do Not Smoke but of Fathers

Newborns of mothers who do not smoke but of fathers who do smoke tend to be smaller than average.Why?

A) Fathers who smoke create unnecessary stress for their pregnant partner, and this increased level of stress affects fetal growth.
B) Smoking in the father alters his DNA, which differentially affects fetal growth.
C) Fathers who smoke tend to be smaller than average themselves.
D) The pregnant woman becomes a "passive smoker" when living with a smoker.