Fact 1: Shivering occurs when many muscles contract a little bit all at once.

Fact 2: Another response to cold is shivering.

Given the two facts above, answer the question "Many muscle fibers contracting at once can be induced by" with the following options: 
- exposed genitalia
 - exposure to heat
 - sweating
 - exposed biceps
 - mechanical waves
 - Electrical energy
 - exposure to cold
 - Veins and arteries.


 

       exposure to cold  