题目内容
16．About a century ago，the average life-span （寿命） for Americans was about 50 years．Today，the typical American lives for around seventy-eight years．According to a German aging study，the maximum life span in industrialized countries has increased by two years every decade since the mid 19th century．What accounts for such increased longevity？Between 1900 and 1950，inventions such as refrigeration（制冷技术）and sewage treatment（污水处理） meant that young people were able to survive longer．Moreover，medical breakthroughs helped contain diseases such as polio（小儿麻痹症），which killed many children．These advances helped increase the average life span．
Medical discoveries after World War II tended to benefit older people．Treatments for heart disease，for example，have allowed the elderly to live longer on average．So does this mean that future medical breakthroughs will result in even longer average life spans，or have we reached our limit？Scientists disagree．
Some argue that if science is one day able to remove disease and old-age infirmity，there will be virtually no limit on how long humans can live．Some even predict that by the year 2150，the average life span will have increased to around 120 years．
Other life-expectancy researchers find that scenario（假设） highly unlikely．Our bodies'cells can keep reproducing for only so long before they peter out（分裂）．Only when science finds a way to keep our cells dividing longer will we see another significant leap in life expectancy．
Still，with plenty of exercise and a healthy diet，those who hold the view can always hope that they'll live long enough to break the record held by Jeanne Louise Calment of France，who lived to be 122．
28．Compared with the average life-span about a century ago，the typical American lives about
C years longer at present．
A.50
B.78
C.28
D.42
29．After World War II，the longer average life spans mainly resulted fromB．
A．refrigeration and sewage treatment
B．medical breakthroughs
C．keeping the cells dividing longer
D．reducing polio
30．What is the scientists'attitude towards the view"we have reached our life-span limit"？D
A．supportive
B．objective
C．optimistic
D．disapproving
31．According to some life-expectancy researchers，keeping our bodies'cells reproducing before they peter out may beA．
A．impossible
B．possible
C．exciting
D．concerning．
分析 本文是一篇科教类阅读，属于说明文，大约一个世纪前，美国人的平均寿命约为五十年．今天，典型的美国人的寿命约七十八年．本文以此展开讨论，主要讲述了不同时期人们的平均寿命增加的原因．
解答 28．C．细节理解题．根据About a century ago，the average life-span （寿命） for Americans was about 50 years．Today，the typical American lives for around seventy-eight years．可知，一个世纪前，平均寿命是50，现在是78．故现在比原来长28．故选C．
29．B．细节理解题．根据Medical discoveries after World War II tended to benefit older people．可知，在世界第二次大战期间是医学突破有利于人们的寿命．故选B．
30．D．推理判断题．根据So does this mean that future medical breakthroughs will result in even longer average life spans，or have we reached our limit？Scientists disagree．可知，作者对于我们已经达到了寿命极限是不支持．故选D．
31．A．细节理解题．根据Other life-expectancy researchers find that scenario（假设） highly unlikely．Our bodies'cells can keep reproducing for only so long before they peter out（分裂）．Only when science finds a way to keep our cells dividing longer will we see another significant leap in life expectancy．可知，其他预期寿命的研究人员发现，假设非常不可能．我们的身体细胞只有在分裂之前才能保持繁殖．只有当科学找到一种保持细胞分裂更长时间的方式，我们才会看到另一个重要的飞跃预期寿命．故选A．
点评 本文是一篇科教类阅读，题目涉及多道主旨大意题，细节理解题，推理判断题．做题时学生应仔细阅读原文，把握文章主要内容，联系文章上下文内容并结合所给选项含义，从中选出正确答案，一定要做到有理有据，切忌胡乱猜测．
