To understand the unusual behavior of an adult client,a clinical psychologist carefully investigates the client's current life situation and his physical,social-cultural,and educational history. Which research method has the psychologist used?

A) the survey
B) the case study
C) experimentation
D) naturalistic observation

The psychologist has used the case study method, which involves in-depth investigation of an individual or a small group. This method is used to understand unusual behavior, and involves the careful examination of a person's current and past life situation, as well as their physical, social-cultural, and educational history. The survey method involves collecting data from a large group of people using standardized questionnaires, while experimentation involves manipulating variables to establish cause-and-effect relationships. Naturalistic observation involves observing people in their natural environment, without manipulating any variables.