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　　连接词

　　1. 含义：
　　主要考察连词的句内关系和副词的句间关系。
　　2. 类型：
　　(1) 从属连词的句内关系
　　① 连词although、though 引导让步状语从句连词if、unless引导条件状语从句；
　　② 连词because、as、since引导原因状语从句;
　　③ 连词when、while、before、after、until、since、as soon as等引导时间状语从句。
　　3.  用法
　　(1) 从属连词
　　由于从属连词将从句与主句连接起来，从句不可独立，是依附于主句，因此:
　　1）从属连词引导的从句在主句前时，从句后要用逗号;
　　2）从句在主句后时，通常无逗号;
　　3）从属连词前后都无逗号；
　　4）两句仅需要一个连词。
　　例如 1：Because Tom likes drinking coffee, he normally buys one from the cafe.
　　（because引导的从句在主句前，要用逗号隔开。）
　　例如 2：Tom was late for work because he missed the train.
　　（because引导的从句“because we missed the bus”在主句后面，此时不用逗号。）
　　以上两个句中because前后都无逗号。
　　例如 3：Because Tom likes drinking coffee, and he normally buys one from the cafe. ?（because连接两句，无需再加连词and。）
　　所以，连词前面后面要不要加逗号，要依据情况而定。

　　真题检测

　　真题检测1
　　(16-11AS Q26) While rare works were tucked away in libraries around the world and many are now also a click away on the Internet.
　　A. NO CHANGE
　　B. world;
　　C. world,
　　D. world however,
　　解析：通过句首的while看出是连词的考点，根据“从属连词引导的从句在主句前时，从句后要用逗号”的原则排除选项C；又根据“两句仅需要一个连词”的原则排除所以排除选项A和D，所以选B。
　　注：16-11AS Q26指2016年11月亚太的第25题，下同。

　　真题检测2
　　(17-08NA Q21) Although Duchenne made his observation about the orbicularis oculi enjoyment smiles as far back as 1862, it has been only in the recent past that empirical evidence has confirmed the existence of there being a high correlation between the contraction of the muscle and self-reported positive moods along with neural activity consistence with positive emotional states.
　　A. NO CHANGE
　　B. but it has
　　C. while it has
　　D. it having
　　解析：通过句首although等看出是连接词的考点，根据“两句仅需要一个连词”，排除B/C选项；而D选项有无谓语动词，句子结构不完整，也排除，所以选A。

　　真题检测3
　　(17-10NA Q12) While fare-free policies do increase ridership, but they have not been found to be an effective way to address traffic problems.
　　A. NO CHANGE
　　B. ridership, and while
　　C. ridership,
　　D. ridership;
　　解析：通过句首while等看出是连接词的考点，根据“两句仅需要一个连词”，排除A./B选项；又根据“从属连词引导的从句在主句前时，从句后要用逗号”排除D，所以选C。

　　真题检测4
　　(17-10NA Q12) Advocates of fare-free policies claim that the costs of these policies are largely offset by various savings, however, a recent study comparing projected results of fare-free policies in different cities found this outlook to be way too sunny.
　　A. NO CHANGE
　　B. savings,
　　C. savings, but
　　D. savings; and
　　解析：通过选项but等看出是连接词的考点，however是副词，不能单独分隔两个独立句，所以排除选项A；而逗号不能单独分隔两个独立句，所以排除选项B；分号和and都可以分隔两个独立句，因此重复，所以排除D；又根据“两句仅需要一个连词”，所以选C。

　　真题检测5
　　(17-10NA Q12) Dried collodion is unusable, so once the photo is snapped with a massive, tripod-mounted camera, the photographer has nominal minutes to develop it, using more chemicals.
　　A. NO CHANGE
　　B. but
　　C. and
　　D. for
　　解析：通过选项so等看出是连接词的考点，前半句说火棉胶一旦干了就无法用了，后半句说摄影师有几分钟去发展它，所以前后是因果关系，排除选项B/C/D，所以选A。