A． Make a survey on employees' preference on different shifts.
B． Give a physical test and find those who are always energetic at nights.
C． Stick to the pattern for three months once the shifts are settled down.
D． Look for those who can adjust fast to the change of wakefulness and sleep.
A． plays a vital role in selecting people for alternative day and night shifts
B． changes every two hours during the day and every three hours during the night
C． has been used for industries in selecting people for alternative shifts
D． changes after a person has finished the training for alternative shifts