对等连接词（主要是and，or与but三个）用来连接句子中对等的两个部分，要求对得越工整越好，我们从12个例子中学习这些重要的规则。这些句子都很长，还需要慢慢体会：

例1：

The Yangtze River, the most vital source of irrigation water across the width of China and important as a transportation conduit as well, has nurtured the Chinese civilization for millennia.（错误）

（长江是横贯中国最重要的灌溉水源，同时也是重要的交通管道，数千年来孕育着中华文化）

这里and连接的两个部分，the most vital source是：

The Yangtze River, the most vital source of irrigation water across the width of China and an important transportation conduit, has nurtured the Chinese civilization for millennia.

例2：

Scientists believe that hibernation is triggered by decreasing environmental temperatures, food shortage, shorter periods of daylight, and by hormonal activity.（错误）

科学家认为引发冬眠的因素包括环境的气温下降、食物短缺、白昼缩短以及荷尔蒙作用

句子的结构是A、B、C、and by D，四个部分应该都是平行的，应该放置于单一的介词之后形成by A、B、C、and D结构：

Scientists believe that hibernation is triggered by decreasing environmental temperatures, food shortage, shorter periods of daylight, and  hormonal activity.

例3：

Smoking by pregnant women may slow the growth and generally harm the fetus.（孕妇吸烟可能妨碍胚胎发育，对胚胎照成一般性的伤害）（错误）

这个句子是下面这个句子的简化：

Smoking by pregnant women may slow the growth of the fetus, and it may generally harm the fetus.

两个句子有 共同的fetus，但是前面的句子fetus是of的宾语，后一个句子fetus是harm的宾语，前面的句子固然可以省略掉fetus，但是要保留原来的of。正确的写法是：

Smoking by pregnant women may slow the growth of and generally harm the fetus.

例4：

Rapid advances in computer technology have enhanced the speed of calculation, the quality of graphics, the fun with computer games, and have lowered prices.

从内容上讲前三个部分A、B、C是增加的部分，最后一个lowered prices是减少的部分，不适合使用对等连接词and。应修改为：

Rapid advances in computer technology have enhanced the speed of calculation, the quality of graphics and the fun with computer games while lowering prices.

例5：

Population density is very low in Canada, the largest country in the Western Hemisphere and it is the second largest in the whole world.

and连接的两个部分中，虽然在意义上是对称的，但是结构上不对称：

Population density is very low in Canada, the largest country in the Western Hemisphere and the second largest in the whole world.

例6：

Once the safety concerns over the new production procedure were removed and with its superiority to the old one being proved, there was nothing to stop the factory from switching over.（新的生产程序一旦排除安全方面的顾虑，并且证明它比旧的生产程序更好，这家工厂就没有理由不作改变了）

and连接的两个部分还原为：

The safety concerns over the new production procedure were removed and its superiority the old one was proved.

重复部分的be动词可以省略成：

Once the safety concerns over the new production procedure were removed and its superiority to the old one proved, there was nothing to stop the factory from switching over.

例7：

Worker bees in a honeybee hive assume various tasks, such as guarding the entrance, serving as sentinel and to sound a warning at the slightest threat, and exploring outside the nest for areas rich in flowers and consequently nectar.

黑体部分的B1和B2与原有的A、C不对称，修改为：

Worker bees in a honeybee hive assume various tasks, such as guarding the entrance, serving as sentinel and sounding a warning at the slightest threat, and exploring outside the nest for areas rich in flowers and consequently nectar.

例8：

Shi Huangdi of the Qin dynasty built the Great Wall of China in the 3rd century BC, a gigantic construction that meanders from Gansu province in the west through 2400km to the Yellow Sea in the east and ranging from 4 to 12 m in width.

同样的道理，and的右边同左边不对称，修改为：

Shi Huangdi of the Qin dynasty built the Great Wall of China in the 3rd century BC, a gigantic construction that meanders from Gansu province in the west through 2400km to the Yellow Sea in the east and ranging ranges from 4 to 12 m in width.

例9：

The large number of sizable orders suggests that factory operations are thriving, but that the low-tech nature of the processing indicates that profit margins will not be as high as might be expected.

对等连接词but连接的是：

句1：The large number of sizable orders suggests something good.

句2：The low-tech nature of the processing indicates something bag.

but的右边应该与左边的主要从句对称，不应该使用that来引导。

例10：

Not only is China the world's most populous state but also the largest market in the 21st century

像not……only与but also之间的对等连接词要求更为严格，改成倒装句以后，but右边只有了名词短语，应该修改为完整的从句：

Not only is China the world's most populous state but it is also the largest market in the 21st century.

例11：

New radio stations are either overly partisan, resulting in lopsided propaganda, or avoid politics completely , shirking the media's responsibility as a public watchdog.

either……or的两个部分词性不一样，应该统一修改成形容词：

New radio stations are either overly partisan, resulting in lopsided propaganda, or completely apolitical, shirking the media's responsibility as a public watchdog.

例12：

Many modern-day scientists are not atheists, to whom there is no such thing as God; rather agnostics, who refrain from conjecturing about the existence of God, much less his properties.

原句使用的是；和rather来连接，分号可以代替两个连接词来连接从句，但是不能取代对等连接词来连接名词短语，所以要使用not……but词组：

Many modern-day scientists are not atheists, to whom there no such thing as God, but agnostics, who refrain from conjecturing about the existence of God, much less His properties.