In a study begun in 1965, a group of 3,000 adults in Baltimore were asked about alcohol consumption. The occurrence of cases of cancer between 1981 and 1995 was studied in this group. This is an example of:
a. A cross-sectional study
b. A prospective cohort study
c. A retrospective cohort study
d. A clinical trial
e. A case-control study
Answer: b. A prospective cohort study