Fact 1: Sound can be used for communication by animals.

Fact 2: Sound Sound waves are mechanical waves.

Given the two facts above, answer the question "What can be used for communication by animals?" with the following options: 
- books
 - Electrical energy
 - electromagnetic energy
 - nails
 - chemical messengers
 - mechanical waves
 - encoded information
 - ice


 

      mechanical waves   