Answer to Question 1
All differential reinforcement procedures use extinction for undesirable behavior. Thus, one mechanism that decreases the undesirable response is extinction. However, differential reinforcement also uses reinforcement for either incompatible, alternate, other, or low rates of behavior. If a behavior incompatible with the undesirable behavior is increased, the undesirable behavior must decrease. When alternate or other behaviors are increased, this typically results in a decrease in undesirable behavior.
Answer to Question 2
A