现在，我们已经清楚地了解了单句的结构，并且可以用语法知识自行造句。接着我们就开始学连词，以延伸或扩展句子的内容。
中文句子可允许双连词的存在，如下例：
因为现在正在下雨，所以我们只好待在家里。
然而在英语句子结构中，两句只能使用一个连词，所以我们不能说：
|Because/As/Since| it is raining now, wo we have to stay home.（×）
因此，如果句首已经有Because、As或Since（均表示“由于”或“因为”），连词so就应删除，反之亦然。
|Because/As/Since| it is raining now, we have to stay home.
（因为现在正下着雨，所以我们不得不待在家里。）
It is raining now, so we have to stay home.
（现在正在下雨，因此我们不得不待在家里。）
同理：连词although（虽然）、even though（虽然）、though（虽然）、even if（即使）与but（但是）也不能并存，否则会造成双重连接的错误句子结构，请参看下例：
Although Mary is pretty, but there is no chemistry between us.（×，Although与but不应并存）
应改为：
Although Mary is pretty, there is no chemistry between us.
（虽然玛丽很美，我俩却没缘分。）
=Mary is pretty, but there is no chemistry between us.
（玛丽很美，不过我俩却没缘分。）
注意：英语中有下列所谓的连接副词，这些副词有连词的意味，却仍是副词而非连词，所以使用时副词后应加逗号，并以分号或句号连接两个句子：
（a）有连词but意思的连接性副词：
however（然而）、nonetheless（但是）
（b）有连词so意思的连接性副词或副词词组：
therefore（因此）、consequently（因此）、as a consequence（因此）、as a result（因此）
（c）有连词and意思的连接性副词或副词词组：
moreover（此外）、furthermore（此外）、in addition（此外）、besides（此外）
The job is difficult, but you should at least give it a try.
=The job is difficult; however, you should at least give it a try.
=The job is difficult; nonetheless, you should at least give it a try.=The job is difficult. However, you should at least give it a try.
=The job is difficult. Nonetheless, you should at least give it a try.
（这工作很困难，不过你至少应试试看。）
John studied very hard, so he passed the test.
=John studied very hard; therefore, he passed the test.
=John studied very hard; consequently, he passed the test.
=John studied very hard; as a consequence / in consequence, he passed the test.
=John studied very hard; as a result, he passed the test.
（约翰很用功，因此他考试及格了。）
Mary sings well, andshe is good at playing the piano.
=Mary sings well; moreover, she is good at playing the piano.
=Mary sings well; furthermore, she is good at playing the piano.
=Mary sings well; in addition, she is good at playing the piano.
=Mary sings well; on top of that, she is good at playing the piano.
（玛丽歌唱得很好，而且她也弹得一手好钢琴。）
Stay away from Paul. He is selfish, and he tends to lie.
=Stay away from Paul. He is selfish; besides, he tends to lie.
（远离保罗。他为人自私，而且他也爱说谎。）
由上得知，我们可借助连词或连接性副词将句子延伸，增加句子的内容，同时也可以奠定写长文的基础。语法学到这个地步我就开始进入每天写日记的阶段，把每天学到的单词、例句及造句的基本语法知识加以结合，再用写日记的形式表现出来。
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