It can be inferred from the passage that brain size is assumed to ______.

A．Body temperature may serve as an indication of a worker's performance.
B．The selection of a number of permanent night shift workers has proved to be the best solution to problems of the round the clock working system.
C．Taking body temperature at regular intervals can show how a person adapts to the changes of routine.
D．Disturbed sleep occurs less frequently among those on permanent night or day shifts.

A．Because few people like to reverse the cycle of sleep and wakefulness.
B．Because sleep normally coincides with the hours of darkness.
C．Because people are required to work at night in some fields of industry.
D．Because shift work in industry requires people to change their sleeping habits.