In a Study of the Effectiveness of a Treatment for Depression,a

Multiple Choice

In a study of the effectiveness of a treatment for depression,a psychologist assessed patients' symptoms of depression using a reliable questionnaire both before and for several months after treatment.The results indicated that the patients experienced a decrease in their symptoms over the 8-month time period of the study.One threat to internal validity the researcher should consider is

A) maturation.
B) regression.
C) testing.
D) all of these