Fact 1: Caffeine is a central nervous system stimulant.

Fact 2: Coffee is an excellent source of caffeine.

Given the two facts above, answer the question "what is a central nervous system stimulant?" with the following options: 
- blood
 - NaCl
 - SO2
 - coffee
 - h2o
 - salt
 - vinegar
 - A drug.


 

    coffee     