Answer the following question given this paragraph: 

In order to live on land and in water, frogs have three eyelid membranes: one is see-through to protect the eyes underwater, and the two other ones let them see on land. Frogs also have a tympanum , which acts like a simple ear. They are found on each side of the head. In some species, the tympanum is covered by skin.


Q: How many eyelid membranes do frogs have?


A:
three