Which of the Following Is True with Regard to Case

Which of the following is true with regard to case studies?

A) Classic studies in early abnormal psychology rarely used the case study as a reliable research method.
B) The case study method is ideal for researchers who intend to conduct an intensive investigation of an individual or a small group of individuals.
C) An in-depth case study involves high experimental control and is likely to make a useful addition to the literature.
D) Investigators using case studies must adopt a subjective approach in order to obtain the best results.