I'm stuck between D and E.
d) more rapidly during dreams than during the period of time when a person is awake
Well formed sentence. But we are talking about eye movement when waking up not when a person is entirely awake.
e) more rapidly when dreaming than when waking
This seems to be the best answer. Although it can be better written...more rapidly when dreaming than when a person is waking up.
I go for E.
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