A
Here is an astonishing and significant fact: Mental work alone can't make us tired. It sounds absurd. But a few years ago, scientists tried to find out how long the human brain could labor without reaching a stage of fatigue (疲劳)．To the amazement of these scientists, they discovered that blood passing through the brain, when it is active, shows no fatigue at all! If we took a drop of blood from a day laborer, we would find it full of fatigue toxins(毒素) and fatigue products. But if we took blood from the brain of an Albert Einstein, it would show no fatigue toxins at the end of the day.
So far as the brain is concerned, it can work as well and swiftly at the end of eight or even twelve hours of effort as at the beginning. The brain is totally tireless. So what makes us tired?
Some scientists declare that most of our fatigue comes from our mental and emotional (情感的) attitudes. One of England's most outstanding scientists，J. A. Hadfield，says，“The greater part of the fatigue from which we suffer is of mental origin. In fact, fatigue of purely physical origin is rare. ” Dr. Brill, a famous American scientist，goes even further. He declares，“One hundred percent of the fatigue of a sitting worker in good health is due to emotional problems. ”
What kinds of emotions make sitting workers tired? Joy？Satisfaction？No！A feeling of being bored，anger，anxiety，tenseness, worry, a feeling of not being appreciated—those are the emotions that tire sitting workers. Hard work by itself seldom causes fatigue. We get tired because our emotions produce nervousness in the body.
【解题导语】 本文为一篇说明文，主要介绍了一项惊人的发现：脑力工作本身不会使人感到疲劳。
21．What surprised the scientists a few years ago?
A．Fatigue toxins could hardly be found in a laborer's blood.
B．Albert Einstein didn't feel worn out after a day's work.
C．The brain could work for many hours without fatigue.
D．A mental worker's blood was filled with fatigue toxins.
解析：选C 细节理解题。根据第一段中的“To the amazement of these...shows no fatigue at all！”可知，让科学家惊讶的是大脑工作时不会显示出疲劳，故选C项。
22．According to the author, which of the following can make sitting workers tired?
A．Challenging mental work.
B．Unpleasant emotions.
C．Endless tasks.
D．Physical labor.
解析：选B 细节理解题。根据第三段最后一句话可知，导致我们疲劳的主要是不良的情绪，故选B项。
23．What's the author's attitude towards the scientists' ideas?
A．He agrees with them.
B．He doubts them.
C．He argues against them.
D．He hesitates to accept them.
解析：选A 观点态度题。结合全文尤其是文章第一句话可知，作者对这一新的科学发现虽然感到震惊但又认为它是一个具有重要意义的事实，故选A项。
24．We can infer from the passage that in order to stay energetic, sitting workers need to ________.
A．have some good food
B．enjoy their work
C．exercise regularly
D．discover fatigue toxins
解析：选B 推理判断题。由文章最后两段可知，导致我们疲劳的主要是不良的情绪，因此要想保持活力必须保持愉悦的心情，故选B项。
