When people are experiencing vivid dreams:
a. their bodies often move in accordance with what they dream.
b. their eyes are likely to move under their closed eyelids.
c. they are more likely to sleepwalk than during any other stage of sleep.
d. their slow brain-wave patterns indicate that they are deeply asleep.
e. they intermittently stop breathing.

b. Their eyes are likely to move under their closed eyelids.

Explanation:

Vivid dreaming is the term referring to our conscious awareness of a particular state or condition as we dream, resulting in an experience from which we have a very clear and vivid memory, usually appearing to have direct control and ability over our actions, and some sometimes the unfolding of the dream content itself.

Since a vivid dream represents a state of consciousness, it is possible for the person who is having these dreams to move their eyes under closed eyelids.