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．to change shifts at longer intervals
B．to have longer shifts
C．to arrange for some people to work on night shifts only
D．to create better living conditions for night workers