单选题 {{B}}Questions 21-25based on the following passage:{{/B}}

As people continue to grow and age, our body systems continue to change. At a certain point in your life your body systems will begin to weaken. Your joints may become stiff. It may become more difficult for you to see and hear. The slow change of aging causes our bodies to lose some of their ability to bounce back from disease and injury. In order to live longer, we have always tried to slow or stop this process that leads us toward the end of our lives.
Many factors contribute to your health. A well-balanced diet plays an important role. The amount and type of exercise you get is another factor. Your living environment and the amount of stress you are under is yet another. But scientists studying senescence (衰老) want to know: Why do people grow old? They hope that by examining the aging process on a cellular level medical science may be able to extend the length of life.

单选题 When people become aging, they will lose some of their ability to bounce back from disease and injury, "bounce back" here means ______。

【正确答案】 A

【答案解析】[注释] 人体随着年龄的增长，身体各系统不断变化，衰老的缓慢发展使机体失去了对疾病和伤害做出反应的某些能力。

单选题 In order to live longer,

单选题 Why are some scientists interested in studying senescence?

A、 They want to increase the general ability of our bodies.
B、 They may be able to find a better way to our life.
C、 If they can pin down the biochemical process that makes us age, there will be hope for extending the length of life.
D、 They want to find out if there is a link between how efficiently a cell could repair itself and how long a creature lives.

单选题 Which of the following is NOT mentioned as a factor contributing to one's health?

【正确答案】 B

【答案解析】[注释] 本题的关键是找到选项的信息在文章中出现的地方，也就是第2段的前半段。应该将每一个选项的内容与原文相对应。只有B选项的意思不同于原文中“The amount and type of exercise you get is another factor．”这个句子的全部和确切含义，所以就可以确定 B选项为正确选项。

单选题 This passage is mainly concerned with ______.

【正确答案】 A

【答案解析】[注释] 本题的关键是找到主题句，确定短文的中心思想。一般而言，主题句是文章的第一个句子。此题的正确选项是A，符合主题句的意思。其他的选项都是本短文的细节信息。