Fact 1: Matter vibrating can cause sound.

Fact 2: When the waves pass our ears, a sound is detected.

Given the two facts above, answer the question "What can our ears detect?" with the following options: 
- extremely high frequencies
 - matter vibrating
 - population movement
 - extremely high-pitched sound
 - electromagnetic energy
 - matter's height
 - sensory neurons
 - rays or beams


 

  matter vibrating       