41.
（a） he was taking a walk.
（b） he was talking to professor calhoun.
（c） he was having problems with his car.
（d） he was eating dinner.
42.
（a） admission forms.
（b） solar energy.
（c） auto maintenance.
（d） course requirements for engineers.
43.
（a） three.
（b） four.
（c） five.
（d） six.
44.
（a） one.
（b） two.
（c） three.
（d） four.
45.
（a） drive her to the lecture.
（b） let her give him a ride.
（c） borrow her car.
（d） get his car repaired.
46.
（a） to make recommendations on sensible dieting.
（b） to report the latest advances in brain surgery.
（c） to relate an experiment combining sleep and exercise.
（d） to advise on ways of dealing with sleep difficulties.
47.
（a） your heart rate is lowered.
（b） it becomes harder to relax.
（c） you become too tired to sleep.
（d） sleep rhythms are disrupted.
48.
（a） failure to rest during the day.
（b） lack of sleep on weekends.
（c） vigorous exercise in the evening.
（d） eating cheese before going to bed.
49.
（a） they might eventually cause you to lose sleep.
（b） they help produce a neurotransmitter in the brain.
（c） you must not drink milk if you take them.
（d） they make it unnecessary to take naps.
50.
（a） at a radio station.
（b） in a lecture hall.
（c） in a biology lab.
（d） at the doctor's office.