Ana Is Taking Part in an Experiment in Which She

Ana is taking part in an experiment in which she has agreed to be completely isolated in a room with no windows or clocks for seven days. The lights in the room will be on constantly, and she can call and ask for food whenever she feels hungry. Normally Ana falls asleep around 10:00 p.m. What would you expect to happen to her sleep pattern after seven days of being cut off from external time cues?

A) She would fall asleep at approximately 11:30 p.m., 1 1/2 hours later than normal.
B) She would still fall asleep at approximately 10:00 p.m., but sleep longer.
C) She would fall asleep at 8:30 p.m., 1 1/2 hours earlier than normal.
D) She would sleep for only a few hours at a time, several times each day.