文段落中的各个语句在长度上应该有一定变换，即所谓的长短句之说。短句给人以精炼强调之感，长句则给人以严谨深刻之感。一般说来，长句有两种情况，一种是由于结构复杂而形成的长句，多见于书面语；还有一种是由简单句扩展而成以使语句表达得更加生动和清楚，主要出现在口语的表达中。

例如，有人曾请两个人用英文表达同一内容：“今有一物，不知其数，三三数之余二；五五数之余三；七七数之余二。问物几何?”第一个人的英文表达很书面化：
We have a number of things which, counted by threes, leave two; by fives, leave three; and by sevens, leave two. Find the number.

第二个人的英文表达使用了比较长的语句：
We have things of which we do not know the number. If we countthem by threes, they leave a remainder of two. If we count them by fives, they leave a remainder of two. If we count them by sevens, they leave a re-mainder of two. How many things are there?

英文写作不能一味地使用短句。段落中的短句过多，不仅使得段落显得单调，而且使得段落非常零散、内容浅薄。如果一旦发现段落中尽是写短句的话，这时就需要将某些简短的语句扩展成比较长的句子。语句的扩展主要是在语句的主干上增添修饰成分(如定语、状语等)。

有些语句适宜用增添修饰成分的方法进行扩展，但增添修饰成分不应有斧凿之痕，应该使原句更加感觉有血有肉。

1 )You should stop smoking now.
你现在应该戒烟了。

如要扩展此句，可以这样进行：
"You should give up smoking now, for the sake of your own health, forthe sake of the health of others, for the sake of your family, and for the sake of the entire world. "
为了你自己的健康，为了他人的健康，为了你的家庭，也为了整个世界，你现在应该戒烟了。

2) Doctors think that an active person should have a restful hobby, while a person who sits at a desk should have a lively hobby.
医生认为爱好活动的人应该有安静型的业余爱好，而伏案工作的人应该有着活动型的业余爱好。

如要扩展此句，可以这样来进行：
Doctors think that an active person, such as a baseball player or a swimmer, should have a restful hobby such as reading, collections of stamps, dolls, buttons or shells, etc. , while a person who sits at a desk all day, such as a teacher or a doctor should have a lively hobby such as ten-nis, golf, swimming or skating.
医生认为，像棒球选手或游泳运动员这类爱好活动的人应该有安静型的业余爱好，比如阅读、收藏邮票、收藏布娃娃、收藏钮扣、收藏贝壳等，而整日伏案工作的人如教师或医生，就应该有打网球、打高尔夫球、游泳或者滑冰这类活动型的业余爱好。

3 )A child with a problem will probably go to his friends for sympathy.
一个碰到问题的孩子有可能到朋友那里寻求同情。

如要扩展此句，可以这样来进行：
A child with a problem, then he feels what he will probably get from his parents is incomprehension or criticism, will go instead to his friends for sympathy and advice, leaving the parents totally unaware¹ of the problem he has.
一个碰到问题的孩子，当他觉得他从他的父母那里得到的有可能是不理解或者批评的时候，就会去找他的朋友们寻求同情和建议，而其父母对其问题却全然不知。

4) We can be informed of a lot by reading books.
通过阅读书籍我们可以了解很多东西。

如要扩展此句，可以这样来进行：
By reading scientific books, we can be informed of many facts; by reading geography, we know the earth' s surface, forms, physical features,ect.; by reading history, we are told of the growth of the nations.
通过阅读科技书籍，我们可以了解许多事实。通过阅读地理，我们知道了地球的表面、结构和地貌特征等。通过阅读历史，我们了解到世界的发展过程。

5) We'd better to keep company with the true friends.
我们最好和对我们有帮助的朋友交往。

如要扩展此句，可以这样进行：
As friends are both helpful and disastrous², it is better to keep company with the true friends who are helpful, encouraging and loyal, but to avoid  those who are mean, stingy and treacherous³.

由于既有有助于我们的朋友，也有有害于我们的朋友，因此我们最好和那些对我们有所帮助、有所鼓励和忠实的真正朋友交往，而要避免和那些庸的、吝啬的、奸诈的人交往。