Beth has noticed that her nine-year-old son, Billy, has trouble going to sleep at night and ...

Beth has noticed that her nine-year-old son, Billy, has trouble going to sleep at night and frequently tosses and turns for hours after she puts him to bed. Billy and Beth could most benefit from a suggestion that they .
 
  a. use mental imagery by picturing relaxing scenes, such as lying on a warm tropical beach, as he gets ready for sleep
  b. limit his intake of caffeine in the afternoons by not drinking coffee after 4 p.m. each day c. try to force sleep by insisting that Billy remain as still and motionless in bed as possible
  d. adopt a regular exercise program and encourage Billy to exercise vigorously shortly before bedtime
  e. establish a regular bedtime routine and consistently go through this routine before sending Billy to bed