Mary Ann, an 18-year-old, has been depressed since she lost her sister in a car accident. She has frequent depressive episodes; these episodes last for days. She often turns hostile. Her family has decided that she needs professional help. The professional who would be most appropriate for Mary Ann is a(n) psychologist.

Which statement is a good description of a model? a) models are a description of nature based only on one or two variables. b) models are testable ideas but they are not very to most people. c) models are a description of nature that predicts more accurately than real events. d) models are an approximiation of a real system that omits all but most essential variables in a system.