How long can human beings live? Most scientists who study old age think that the human body is  1  to live no longer than 120 years. However, 110 years is probably the longest that anyone could hope to live—if he or she is  2  healthy and lucky. Some scientists even say we can live as long as 130 years! Yet, our cells simply cannot continue to reproduce  3 .They wear out, and as a result, we get old and  4  die.

Even though we can't live forever, we are living a  5  life than ever before.In 1900, the average American life span (寿命) was only 47 years, but today it is 75 years!

When does old age begin then? Sixty-­five may be out-­of-­date as the  6  line between middle age and old age. After all, many older people don't begin to experience physical and mental  7  until after age 75.

People are living longer because more people  8  childhood.Before modern medicine changed the laws of nature, many children died of common childhood  9 . Now that the chances of dying  10  are much lower, the chances of living long are much higher due to better diets and health care.

On the whole, our population is getting older. The  11  in our population will have lasting effects on our social development and our way of life. Some people fear such changes will be for the worse, while some see  12 , not disaster. Today, many men and women in their “golden years” are healthy, still active, and young in  13  if not in age.

As our society grows old, we need the  14  of our older citizens. With long lives ahead of them, they need to  15  active and be devoted.

1.

A designed

B selected

C improved

D discovered

解析：选A。A考查动词。A. design 设计；B. select 选择，挑选；C.improve 提高，改善；D.discover发现。根据句意：科学家们认为人体的结构设计决定了人类最多不会活过120岁，故选择A选项。

2.

A completely

B generally

C apparently

D extremely

解析：选D。D考查副词。句意：然而110岁可能是人们希望能活的最长的寿命-如果他非常的健康和幸运。A. completely 完全地；B. generally 一般地；C. apparently 显然地；D. extremely极其，非常。根据句意：如果一个人非常健康而且很幸运，人们希望能活到110岁。故选择D选项。

3.

A rapidly

B harmlessly

C endlessly

D separately

解析：选C。C考查副词。A. rapidly 快速地；B. harmlessly 无害地；C. endlessly 无止境地；D. separately 分离地，分开地。根据句意：因为人体的细胞不会无止境地再生，因此人的寿命是有限的。故选择C选项。

4.

A eventually

B hopelessly

C automatically

D desperately

解析：选A。A考查副词。A.eventually 最终；B.hopelessly 没有希望地；C.automatically 自动地；D.desperately绝望地，自暴自弃地。根据句意：他们（细胞）慢慢耗尽，结果我们就会变老最终死亡。故选择A选项。

5.

A busier

B longer

C richer

D happier

解析：选B。B考查形容词。A. busier 更忙的；B. longer 更长的；C. richer 更富有的；D. happier更开心的。根据句意：即使我们不能永久地活着，但是我们的寿命比以前更长了。故选B选项。

6.

A finishing

B guiding

C waiting

D dividing

解析：选D。D考查现在分词。A. finish 完成；B. guide 指导，指引；C. wait 等待；D. divide划分。根据文意:把65岁当做中年和老年的分界线，这已经不适合现在的形势了。dividing line分界线，故选D选项。

7.

A stress

B damage

C decline

D failure

解析：选C。C考查名词。A.stress 压力，压迫；B.damage 损坏；C.decline 衰落，衰弱；D.failure失败。根据句意：现在很多老年人是在75岁之后身体和精神才开始衰弱的，故选C选项。

8.

A survive

B enjoy

C remember

D value

解析：选A。A考查动词。A.survive 幸存；B.enjoy 喜欢，欣赏；C.remember 记得；D.value价值，估价。根据句意：现在人们活得更长因为更多的人从童年中幸存下来。故选A选项。

9.

A problems

B fears

C worries

D diseases

解析：选D。D考查名词。A.problem问题；B.fear恐惧，害怕；C.worry担心；D.disease疾病。根据句意：在现代医学改变了自然的法则之前，很多孩子死于常见的儿童疾病。故选D选项。

10.

A poor

B young

C sick

D quiet

解析：选B。B考查形容词。A.poor 穷的；B.young 年轻的，dying young就是年少死去；C.sick 病的；D.quiet 安静的。根据句意：既然年少夭折的可能性更低了，那么活得更长的机会就更高了，因为有了更好的饮食和医学护理。故选B选项。

11.

A changes

B recovery

C safety

D increases

解析：选A。A考查名词。A.change改变；B.recovery恢复；C.safety安全；D.increases增长，增加。根据句意：人口结构的改变会对我们社会的发展和我们的生活方式有持续的影响。故选A选项。

12.

A dreams

B chances

C strengths

D choices

解析：选B。B考查名词。A.dream梦想；B.chance机会；C.strength力量；D.choice选择。根据句意：一些人担心这个改变将会带来一些坏处，然而还有一些人看到的是机会，而不是灾难。故选B选项。

13.

A mind

B appearance

C voice

D movement

解析：选A。A考查名词。A.mind 心态；B.appearance 外表；C.voice 声音；D.movement移动。根据句意：现在，很多处在“黄金年龄”的男士和女士，身体都非常健康，仍然积极，心态也很年轻。故选A选项。

14.

A protection

B suggestions

C contributions

D permission

解析：选C。C考查名词。A.protection 保护；B.suggestions 建议；C.contributions 贡献；D.permission允许。根据句意：随着我们的社会老龄化，我们需要这些老年公民们的贡献。故选C选项。

15.

A sound

B appear

C turn

D stay

解析：选D。D考查动词。A. sound 听起来；B.appear 好像；出现；C.turn 转，变成；D.stay保持。根据句意：前面还有很长的寿命，他们需要保持积极的心态和奉献的精神。故应选D选项。