The correct option is
C Functional
Frogs use their regular set of eyelids to keep their eyes moist and clean. They have a bottom lid that stays still and an upper lid that blinks. Frogs also have a third eyelid that serves a different purpose. This one, called as the nictitating membrane, is a semitransparent lid that covers the eye completely, helping the frog see underwater and hide from predators.
So, the correct answer is option A.