A Friend of Yours Has Been in a 6-Month Treatment

A friend of yours has been in a 6-month treatment program for drug addiction. He is doing well, and has been free of drugs for a while, but when you pick him up after he is released from the program and bring him back to his usual neighbourhood, he begins to experience drug cravings and withdrawal symptoms. This is most likely because ______.

A) he is exaggerating his feelings to manipulate you into getting him some drugs
B) most treatment programs are only successful after at least a year
C) memories of his previously existing problems have been triggered by the cue of his previous environment
D) classically conditioned compensatory mechanisms have been triggered by the cue of his previous environment