Fact 1: Most invertebrates have a nervous system.

Fact 2: Narcotic analgesics act on the central nervous system to relieve pain.

Given the two facts above, answer the question "How do most analgesics work on invertebrates?" with the following options: 
- insects
 - kinetic
 - adding heat
 - reduce
 - decrease stamina
 - it needs them
 - Relieve pain
 - protect them


 

       Relieve pain  