You Come Across a Friend Who Is Reading a Request

You come across a friend who is reading a request for volunteers to participate in a study of circadian rhythms. Your friend seems puzzled and asks you what the study might involve. You should tell your friend that circadian rhythms are

A) bodily cycles that affect such things as arousal levels and metabolism.
B) patterns of rhyme and meter used in studies of language behavior.
C) birth control techniques.
D) likely to be found on tests of musical intelligence.