Depressants are drugs that depress this part of the body.
a. digestive system
b. lymphatic system
c. reproductive system
d. central nervous system

The answer is letter D.  

Depressants are drugs that affect the central nervous system. This drug when ingested, breaks down inside the body and is absorbed in the bloodstream, which then travels to the brain. As a result motor skills of a person are affected. These are commonly prescribed by psychiatrists who treat patients that have obsessive compulsive behaviors. It is also usually administered to patients in mental clinics to suppress their aggressive and destructive behaviors.