Psychology (心理学) is the study of the mind and mental activities. For example, psychologists are interested in why some things make you sad, but others make you happy. They want to know why some people are shy, but others are quite talkative. They also want to know why people do the things that they do. They test intelligence.Psychologists deal with the minds and behavior of people. Your mind consists of all your feelings, thoughts, and ideas. It is the result of one part of the brain called the cerebrum (大脑). Your behavior is the way you act or conduct yourself. Examples of behavior include shouting, crying, laughing, and sleeping.Several people have been instrumental (有重要作用的) in the field of psychology. Wilhelm Wundt set up the first psychological laboratory in Leipzig, Germany, in 1879. Ivan Pavlov, a Russian, is noted for his experiments with dogs in which he studied their reflexes and reactions. Around 1900, Sigmund Freud stated his theory that people try to repress (压制) any memories or thoughts that they believed were not good.Psychologists should not be confused with psychiatrists (精神病学家). Psychiatrists deal only with mental illness. They are medical doctors who treat people. We may conclude that psychologists （）.

A. study physical diseases as well
B. deal with animals more often than with people
C. are not medical doctors
D. are interested in things that make you sad