The Data in the Previous Question Show a Much Higher

The data in the previous question show a much higher incidence of low birth weight babies from mothers who smoke. This finding is likely to be a reliable one because

A) everyone knows that smoking is a bad thing.
B) the smokers rate of low birth weight is twice that of the non-smokers.
C) the pattern of differences occurs reliably over each of 5 years.
D) there is a general increase in low birth weight over the years.