Fact 1: Hearing is used for sensing sound by animals.

Fact 2: For example, hearing waves are transmitted by fluid in the inner ear.

Given the two facts above, answer the question "what in the inner ear is used for sensing sound by animals?" with the following options: 
- neurons
 - Frogs.
 - tube
 - Frogs
 - fluid
 - fibers
 - energy
 - motors


 

     fluid    