8．Many people think of the brain as a mystery．They don't know much about intelligence and how it works．When they do think about what intelligence is，many people believe that a person is born smart，average，or dumb---and stays that way in the whole life．But new research shows that the brain is more like a muscle---it changes and gets stronger when you use it．And scientists have been able to show just how the brain grows and gets stronger when you learn．
Everyone knows that when you lift weights，your muscles get bigger and you get stronger．A person who can't lift 20pounds when he/she starts exercising can get strong enough to lift 100pounds after working out for a long time．That's because the muscles become larger and stronger with exercise．And when you stop exercising，the muscles shrink and you get weaker．That's why people say"Use it or lose it!"
But most people don't know that when they practice and learn new things，parts of their brain change and get larger a lot like muscles do when they exercise．Inside the cortex（皮层） of the brain are billions of tiny nerve cells，called neurons．The nerve cells have branches connecting them to other cells in a complicated network．Communication between these brain cells is what allows us to think and solve problems．When you learn new things，these tiny connections in the brain actually multiply and get stronger．The more you challenge your mind to learn，the more your brain cells grow．Then，things that you once found very hard or even impossible to do----like speaking a foreign language----seem to become easy after learning them for a period of time．The result is a stronger，smarter brain．
Scientists started thinking that the human brain could develop and change when they studied animals'brains．They found out that animals that lived in a challenging environment were more"perspicacious"-----they were better at solving problems and learning new things．
71．According to the first paragraph，C．
A．our brain can remember many more things than we think
B．until now it's impossible to explain the brain's mystery
C．many people believe one's intelligence is naturally determined
D．scientists are carrying out many experiments to study intelligence
72．Training muscles is compared toA．
A．developing the brain
B．doing physical exercise
C．remembering things
D．learning a new language
73．What is Paragraph 3mainly about？D
A．How scientists find the secrets of the brain．
B．How changes in the muscles affect the brain．
C．The importance of the brain．
D．How the brain works．
74．What does the underlined word"perspicacious"in the last paragraph probably mean？B
A．strong
B．smart
C．popular
D．active
75．The following paragraph will most probably talk aboutC．
A．differences between animals'brains and humans'brains
B．the right environment to raise animals
C．scientists'findings about animals'brains
D．animals'development throughout history．
分析 本文属于说明文阅读，作者通过这篇文章主要向我们描述了科学研究发现，经常学习能促进大脑的发育，正如经常锻炼能使肌肉更强健一样．
解答 71．C．推理判断题．根据第一段中的"many people believe that a person is born smart，average，or dumb-and stays that way in the whole life"可知很多人认为一个人的智力是天生决定的；故选C．
72．A．细节理解题．根据第一段中的"But new research shows that the brain is more like a muscle-it changes and gets stronger when you use it．"可知训练肌肉被用于比较大脑的发展；故选A．
73．D．段落大意题．根据第三段But most people don't know that when they practice and learn new things，parts of their brain change and get larger a lot like muscles do when they exercise可知本段详细描述了大脑如何通过练习和学习新事物而发生变化，从而变得更敏捷；故选D．
74．B．词义猜测题．根据破折号后面的"they were better at solving problems and learning new things"可知，该词应为"敏锐的"之意；故选B．
75．C．推理判断题．最后一段They found out that animals that lived in a challenging environment were more"perspicacious"-----they were better at solving problems and learning new things提出科学家是从研究动物的大脑得出的结论，因此下一段最可能进一步描述这些研究成果；故选C．
点评 考察学生的细节理解和推理判断能力，做细节理解题时一定要找到文章中的原句，和题干进行比较，再做出正确的选择．在做推理判断题不要以个人的主观想象代替文章的事实，要根据文章事实进行合乎逻辑的推理判断．
