Failing to Account for Age Cohort Effects in Smoking Prevalence

Failing to account for age cohort effects in smoking prevalence may:

A) obscure the fact that older cohorts had higher prevalence of smoking in comparison to younger cohorts.
B) obscure the fact that there had been a shift in the age of onset for lung cancer toward earlier ages.
C) obscure the differences in smoking prevalence for males and females, and by level of education.
D) obscure the fact that there had been a shift in the age of onset for lung cancer toward earlier ages as well as the differences in smoking prevalence for males and females, and by level of education.