Answer the following question given this paragraph: 

The eardrum is like the head of a drum. It is a thin membrane stretched tight across the end of the ear canal. The eardrum vibrates when sound waves strike it, and it sends the vibrations on to the middle ear.


Q: What hits the eardrum and causes it to vibrate?

 Choices:

- cilia

- decibels

- microwaves

- sound waves

A:
sound waves
