What Statement Best Describes a Cohort Study

What statement best describes a cohort study?

A) It focuses on a group of people exposed to a particular health problem or potential stressor over time
B) The researcher manipulates some of the variables in order to ascertain the effect of the manipulation
C) The individuals in the group with the disease are matched with individuals who are similar in some characteristics (e.g., age, gender) but who have not manifested the disease in question
D) Selected variables within a specific population are studied to look for evidence of association and causality