Between ________ of school children suffer from a learning disorder, most commonly ________.

Operant behavior is usually defined as a ______ of responses rather than a specific response.

Fill in the blank(s) with the appropriate word(s).

After surviving an Amtrak derailment, John experienced frequent, vivid thoughts and images of the accident for several months. He also had problems sleeping and was irritable and withdrawn. John is suffering from ________

a. major depression. b. posttraumatic stress disorder. c. generalized anxiety disorder. d. panic disorder.