A、The lack of sleep. B、The difficult question. C、The requirement of your creative thinking. D、The requirement of your original t

Have you ever felt your mind got confused after a sleepless night? You couldn’t come up with an original thought no matter how hard you tried.
    You were probably right if you thought that was caused by a lack of sleep. Dr. Home, a sleep researcher in England, studied 24 college students divided into two groups. One group got their normal eight hours of sleep. The other group didn’t get the smallest amount of sleep--they stayed awake all night. The next day, Dr. Home tested the students. He asked them questions that required creative and original thinking. One of the questions was "How many uses can a cardboard box be put to?"
    The results? The wide-awake students did well on the tests. The tired students did poorly.
    Research has already shown that tired people can do okay on tests of routine thinking, like simple addition. But Dr. Home tested creative thinking only.
    As part of his study, he offered an amount of money as a reward to the sleepy students if they did well. But even this encouragement wasn’t enough to help the students overcome their tiredness. They still did poorly. Dr. Home believes that the cerebral cortex--the part of the brain where thinking takes place--may get worn out during waking hours. Sleep may help to repair the brain overnight. "Without any sleep," he emphasizes, "even if you concentrate harder, you cannot do better." This study gives people something to think about, especially people like hospital workers and airline pilots, who must stay awake all night and then make emergency decisions.