The neurotransmitter associated with regulation of mood, behavior, and thought processes is

serotonin                                                        

Explanation:

Serotonin: The term serotonin refers to a neurotransmitter and a chemical which is produced by nerve cells and is responsible for sending signal between different nerve cells and generally found in the digestive system, blood platelets, and in the central nervous system.

Serotonin helps in regulating social behavior, mood, digestion, memory, sexual functions and desires, and sleep, etc.

In the question above, the given statement signifies the role of serotonin.

answer; conditional stimulus will trigger a conditioned response;

a is your answer hope this ! : )