Life Expectancy in the Last Hundred Years A hundred years ago,life expectancy in developed countries was about 47; in the ea

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问题                 Life Expectancy in the Last Hundred Years
    A hundred years ago,life expectancy in developed countries was about 47; in the early 21st century, men in the United States and the United Kingdom can expect to live to about 74, women to about 80, and these【C1】______are rising all the time. What has brought【C2】______ these changes? When we look at the life【C3】______of people 100 years ago, we need to look at the greatest【C4】______of the time. In the early 20th century, these were the acute and often【C5】______infectious diseases such as smallpox. Many children died very young from these diseases and others, and the weak and elderly were always at risk.
    In the【C6】______world these diseases are far【C7】______today, and in some cases have almost disappeared. A number of【C8】______have led to this: improvements in sanitation and hygiene, the discovery and use of antibiotics, which【C9】______bacterial diseases much less dangerous, and vaccinations 【C10】______common diseases. 【C11】______, people’s general health has improved with improvements in our general environment: cleaner air, better means of preserving food, better and warmer housing, and better understanding of nutrition.
    Genetically ,we should all be able to live to about 85 but【C12】______people do live longer today, there are still some big killers around that are preventing us from consistently reaching that age. The problems that affect people today are the more chronic illnesses, such as heart disease and strokes, and those【C13】______by viruses, such as influenza and AIDS. Of course, cancer is a huge killer as well. In most cases these diseases affect【C14】______people, but there are worrying trends in the developed world with problems such as obesity【C15】______more heart disease and illnesses such as diabetes at younger ages.
    The killers today can be classed as "lifestyle diseases" ,which means that it may be possible to halt their progress.
【C9】

选项 A、makes
B、causes
C、make
D、cause

答案C

解析 注意这里的which不是非限制定语从句中指代前面一句话的作用,而是指代前面两项内容:卫生的改善和抗生素的发明使用,所以which后的动词不用单三形式。cause没有这样的语法搭配。
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