Duke Is Petrified of Snakes

Duke is petrified of snakes. To help him overcome his fear, his therapist is teaching Duke to relax in the face of increasingly more realistic encounters with a snake. First, Duke simply imagines the snake, then he imagines that a snake placed in a box is brought into the room, and so on, until he finally imagines himself holding the reptile. He implements the relaxation procedures his therapist has taught him each time he imagines a different "snake scenario."Duke's therapist is using the therapeutic technique called

A) rational-emotive therapy.
B) aversion therapy.
C) modeling.
D) systematic desensitization.
E) implosion therapy.