Caffeine is a central nervous system stimulant, and caffeine is a stimulant, and a stimulant constricts blood vessels. Given these facts, what does caffeine do to blood vessels among the following options:
- It expands
 - looseness
 - hydrate their cells
 - Constrict them
 - sweating
 - Dehydration
 - They may not survive.
 - Damages them


 

    Constrict them     