Final answer:
Alcohol (B) is classified as a depressant.
Step-by-step explanation:
The depressant among the given options is alcohol (B).
Depressants are drugs that lower neurotransmission levels in the brain, reducing arousal or stimulation. Alcohol is classified as a depressant, as it suppresses central nervous system activity. Other depressants include barbiturates and benzodiazepines, which share the ability to serve as agonists of the gamma-Aminobutyric acid (GABA) neurotransmitter system.