Stimulants are

A) drugs that speed up activity in the central nervous system.
B) any drug capable of influencing perception, mood, cognition, or behavior.
C) drugs that slow down activity in the central nervous system.
D) drugs derived from the opium poppy which relieve pain and produce euphoria.

Answer: A
Rationale: Stimulants are a category of drugs that speed up the nervous system, typically enhancing wakefulness and alertness. Cocaine and amphetamines are both examples of stimulants. Drugs derived from the opium poppy, which relieve pain and produce euphoria, are naturally occurring opiates, not stimulants.