After cheering wildly at an exciting football game your body may begin to relax on the way home. this relaxation reflects activity of the nervous system.

Answer;

-Sympathetic nervous system

After cheering wildly at an exciting football game your body may begin to relax on the way home. This relaxation reflects activity of the sympathetic nervous system.

Explanation;

The sympathetic nervous system is part of the autonomic nervous system, which also includes the parasympathetic nervous system.

The sympathetic nervous system activates what is often termed the fight or flight response. Like other parts of the nervous system, the sympathetic nervous system operates through a series of interconnected neurons. Sympathetic neurons are frequently considered part of the peripheral nervous system (PNS), although there are many that lie within the central nervous system

i am going to guess that it is co2.