资料题：Which of the following is true according to the passage（　）。

However, when she gets tired she makes mistakes, especially transporting letters, much more frequently.To overcome this she has to raise her level of arousal and concentration but beyond a certain point the automaticity is lost and thinking about hitting the keys leads to more mistakes.Other jobs involve intense concentration such as holding bottles of whisky up to a strong light and turning them upside down to look for particles of dint falling down.This Bounds quite easy but experience teaches that workers can do this for only about thirty minutes before they start making a mistake.This is partly because the number of occasions with dirt in the bottles is low and the arousal level, therefore, falls.Donald Broadbent and his colleagues at the MRC Applied Psychology Unit, Cambridge, have shown that devices to raise arousal level will increase the accuracy of looking for relatively rare events.A recent study of the effect of loss of sleep on young doctors showed that in tests involving a challenge to their medical judgment when short of sleep they raised their arousal level and became better at tests of grammatical reasoning aS well.