Which of the Following Is a Case-Control Study

Which of the following is a case-control study?

A) Analysis of previous research in different places and under different circumstances to permit establishment of a hypothesis based on cumulative knowledge of all known factors identified in the disease under study.
B) Obtaining histories and other information from a group of people with a particular disease or condition and from a group without the disease to determine the relative frequency of a past exposure under study.
C) Defining a group of disease free people by their exposure status and then following up over time to see which ones develop a disease or condition.
D) Study of average exposure for a group and a population measure of outcome.