Although many of us may feel air-conditioners bring relief from hot, humid or polluted outside air, they pose many potential health hazards. Much research has looked at how the movement of air inside a closed environment---such as an office building---can spread disease or expose people in the building to harmful chemicals.

One of the more widely publicized dangers is that of Legionnaire’s disease, which was first recognized inthe 1970s. This was found to have affected people in buildings with air-conditioning systems in which warmair pumped out of the system’ cooling towers was somehow sucked back into the air intake (通风口),in mostcases due to poor design. The warm air, filled with bacteria,was combined with cooled, conditioned air andwas then circulated around various parts of the building. Studies showed that even people outside such buildings were at risk if they walked past air exhaust pipes.

Large air-conditioning systems add water to the air they circulate by means of humidifiers (湿度调节器).Inolder systems, the water used for this process is kept in special reservoirs, the bottoms of which providebreeding grounds for bacteria which can find their way into the ventilation (通风)system. The risk to human health from this situation has been highlighted by the fact that the immune systems (免疫系统)of approximately half of workers in air-conditioned office buildings have developed the ability to fight off the organisms found at the bottom of system reservoirs. But chemicals called “biocides”are added to reservoirs to make them germ-free, and they are dangerous in their own right in sufficient quantities, as they often contain compounds strongly linked to cancers.

Finally, it should be pointed out that the artificial climatic environment created by air-conditioners canalso affect us. In a natural environment, whether indoor or outdoor, there are small variations in temperature and humidity. Indeed, the human body has long been accustomed to these normal changes. In an air-conditioned living or working environment, however, body temperatures remain well under37℃, our normal temperature. This leads to a weakened immune system and thus greater exposure to diseases such as colds and flu.

练习题：

Choose correct answers to the question:

1.What do we know about Legionnaire's disease from the passage?

A.It was the most widely concerned office hazard.

B.It can affect people both inside and outside the building.

C.It happens only in air-conditioned office buildings.

D.It does not develop in well-designed buildings.四级阅读理解技巧

2.In the old air-conditioned systems, bacteria first develop______.

A.in the reservoirs

B. in the ventilation system

c. in the humidifiers

D. in the air intake

3.The fact that about half of workers developed the ability to fight off the bacteria may__.

A.relieve people’s worry about the danger caused by the bacteria

B.help people find an effective way to get rid of the bacteria

C.reflect the serious danger brought by the bacteria

D.cause serious disease such as cancers to people

4.The author most probably wants the readers to treat biocides with an attitude of_.

A.caution

B.trust

C.enthusiasm

D.criticism

5.The last paragraph implies that our immune system can be weakened when _•

A.we live in an artificial climatic environment

B.there are variations in temperature and humidity

C.our body temperatures often remain not high enough

D.we are often exposed to diseases such as colds and flu

1.[B] 事实细节题。本题主要考査复合句的理解。第2段最后一句表明B是正确选项。选项A中的most和C中的only都太绝对了，文中并未对选项A和C中的相关说法加以这样的限定。选项D也太绝对了，第2段第3句只是说到“大多数情况下是因为空调设计欠佳所致”,并不是说所有设计良好的大厦就不会发生这种情况。

2.[A] 事实细节題。本题考查复合句的理解。只要明白第3段第2句这个非限制性定语从句中的the bottoms of which中的which是指上文的reservoirs,问题就不难解决了。

3.[C] 事实细节题。本题考查被动语态长句的理解。在第3段第3句中，关键词是highlight,选项C是对原句主谓部分的近义替换。选项A和B在文中皆无提及，选项D是过度使用生物杀灭剂的后果，与本题干的情况无关。

4.[A] 观点态度题。第3段最后两句讨论生物杀灭剂的用处，其中最后一句中的but, dangerous和cancers等词说明作者认为要慎用这种杀灭剂。作者并没对杀灭剂全盘否定，只是说过量使用会引发危险，因此选项D不对。

5.[C] 推理判断題。本题考查代词的理解。解题的关键在于理解最后一句中的This是指上一句所说的情况。选项A中所说的人造环境不是使免疫系统变弱的必然条件。选项B是保持免疫系统健康的条件。选项D是免疫系统变弱后的影响。