Giovanni’s dog Luna won’t heel. To teach him to heel, Giovanni puts a choke chain and a leash on the dog somewhat tightly and goes for a walk. When Giovanni says "Heel" and Luna walks next to him, Giovanni loosens the choke chain. Now Luna heels much more often than before, due to:
A. positive reinforcement.
B. negative reinforcement.
C. positive punishment.
D. negative punishment.

Now Luna heels much more often than before, due to B. negative reinforcement.

Explanation:

This is a form of Operant Conditioning, in which a behavior is achieved through reinforcements and punishments, positive and negative.

Let's see the terms:

In this case, once Luna heels (the desired behavior), then Giovanni loosens the choke chain which was an aversive stimulus whilst being tight at Luna's neck. Luna's behavior of heeling is increased because of the negative reinforcement.

B. negative reinforcement.

Explanation: Operant conditioning is a form of learning in which the consequences of a behavior determine whether it will be repeated in the future by an organism. Often times behaviors followed by favorable consequences become more likely and those followed by negative consequences become less likely.

Luna heels much more often than before, due to negative reinforcement which is simply a penalty for not doing something. In negative reinforcement, a response or behavior is strengthened by stopping, removing, or avoiding a negative outcome, undesirable consequence or aversive stimulus.