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阅读《勤于用脑》完成后面小题。

    ①常常能听到这样的一种说法:“人的脑子用多了,会死掉许多脑细胞。”“人脑多用了会笨。”这种说法是没有科学道理的。

    ②事实上,人的肌体的各个部位,几乎都是越用越健康,脑子也是一样。让我们先来看一个数据:经科学家研究证明,人的大脑皮层大约有140亿个神经细胞,也叫神经元。这么多数量的脑细胞,对一个人的一生来说足够足够了。有人计算过,如果一个人活到100岁的话。经常运用的脑神经细胞只不过10多亿个,还有80%~90%的脑神经细胞没动用。所以,根本不会有什么“脑子多用会笨”的事情。

    ③“生命在于运动”,这是生物界的一个普遍规律。人的机体,用则灵,不用则衰。脑子用得勤的人,肯定聪明。因为这些勤于用脑的人,脑血管经常处于舒展的状态,脑神经细胞会得到很好的保养,从而使大脑更加发达:避免了大脑的早衰。相反:那些懒于用脑思考的人,由于大脑受到的信息刺激比较少,甚至没有,大脑很可能就会早衰。这跟一架机器一样,搁在那里不用就要生锈,经常运转就很润滑。国外就有过这样的研究,科学家观察了一定数量的20—70岁的人,发现长期从事脑力劳动的人,到了60岁时仍能保持敏捷的思维能力,而在那些终日无所事事、得过且过的懒人当中,大脑早衰者的比例大大高于前者。

    ④除懂得脑子多用只会聪明不会笨的道理以外,我们还应该了解“多用脑,可防老”的道理。这对老年人来讲尤为重要。我们常说,大脑是人体的司令部,如果大脑迟钝了,身体各器官的生理功能当然也不会旺盛。所以,保持大脑的活力,就能促进其他机体、器官保持活力;大脑如早衰,也会影响其他机体、器官的早衰。老年人的健康状况,往往是生理、心理、环境等因素互相影响的结果,老年人保持着勤于用脑的好习惯,就会有一种很好的心理状态,可以使自己的生活、精神充满活力。

    ⑤“勤于用脑,延缓衰老”,这个道理是很科学的。老年人如此,何况我们青少年呢?

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    When high school started, Sally and I became best friends. We shared many interests and quickly became very close.When high school ended, we both cried because we would enter different 1 in autumn.

    Our first term of college life was 2, so we often sent long e-mails and encouraged each other. We missed each other so much! In the second term, I found some new friends and I felt very 3 with them. These were friends with whom I could be myself and pour out my feelings. I wanted to share my new friends with Sally.

    When Sally 4 visited me at my school, we were excited.

    She brought a toy bear to me 5a present and told me about her college life. 6, something unexpected happened when I introduced her to my new friends.Her eyes grew dark and I could see the sadness in them.My new friends tried to share their friendship, but Sally seemed unwilling to accept it.I didn't understand 7the people I loved most couldn't love each other.

    Sally left. I knew she was not happy. I thought long about what had happened. I asked her many questions but she didn't answer me. I 8 that she was jealous(嫉妒). She saw me with my new friends and was afraid that we no longer shared the same experiences. She saw that I could still enjoy myself  9 her and wished she could be a part of it.

    I wrote Sally a letter to 10 she's always my best friend. I told her everyone had friends from home and friends from school, and all the friends were indeed life's greatest 11.Sally wrote me back soon. She was in agreement and felt sorry about 12 she had done.

    I think Sally and I both 13 an important lesson from it. Nothing can influence our 14  and change the experiences we've shared.We are now walking on two different paths of life. While new friends are special and exciting, old friends are 15 there, waiting to share their heart, no matter how far away they are from each other.