As the night progresses, the amplitude of a sleeper's brainwaves _____, and the frequency of the waves _____. a. increases; decreases b. decreases; increases c. increases; increases d. decreases; decreases

I think the correct answer would be D. The brain waves changes from stage 1 to stage 2 as a person sleeps in a way that these waves become slower. That is, the amplitude would  decrease since less activity is done and the frequency would decrease as well since less wave passes per second.