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:
A:
sound waves