A Major Advantage of Cohort Studies Over Case-Control Studies with Respect

A major advantage of cohort studies over case-control studies with respect to the role of a suspected factor in the etiology of a disease is that:

A) they take less time and are less costly.
B) they can utilize a more representative population.
C) it is easier to obtain controls not exposed to the suspected factor.
D) they permit direct determination of risk of disease in those exposed to the suspected factor.
E) they can be done on a double-blind basis.