A cohort study differs from a case-control study in that:

A、Subjects are enrolled or categorized on the basis of their exposure status in a cohort study but not in a case-control study;

B、Subjects are asked about their exposure status in a cohort study but not in a case-control study;

C、Cohort studies require few years to conduct, but case-control studies do not;

D、Cohort studies are conducted to investigate chronic diseases, case-control studies are used for infectious diseases