文章是通過一個一個小篇章來表達思想和主題的，篇章的構造需要詞與句子作為它的基本原料，我們說如果說文章的主題思想是靈魂的話，那句子就是文章無數的血管。血液不通暢文章也就將難成好的文章，我們在對付PETS考試中的作文時，一定要拿捏好以下幾個改句、造句的原則：

　　(一)主題句原則

　　一個好的主題句是文章成功的一半。不僅文章有主題，段落有綱，句也必有中心。文章失卻主題，就會不知所云;落無綱，則一盤散沙，句缺中心，就無意義。所以，在立足于篇章時，一定要首先明確文的主題;在發展段落時，也要首先寫好主題句。從PETS三的特點來考慮，主題句最好是置于文首或段首，這樣讓人一目了然! 以下就是兩個實用的開門見山式發展主題句的方法。

　　●To begin with, we must attach the greatest importance possible to this issue/fact (key word).

　　●As is well known to all, it is now high time that we took this (topic word) into serious consideration.

　　(二) 句式變化原則

　　好的文章動靜結合、張弛有度有節奏感。句式也是一樣，要有變化性，這不僅能使文章更生動，也是語言表達方式的需要和表達能力的體現。句式的變化，主要是要注意兩點：

　　● 不要從頭至尾使用一種句型。

　　● 長短句結合。

　　由于語言功底的欠缺和慣用思維，很多人寫的文章一種句式到頭，如：

　　I think …

　　I hope…

　　He does it.

　　He will take it

　　這樣的文章雖然意思表達出來了，卻顯得呆板，欠生動。解決的辦法是：

　　1.間或使用主從復句。

　　Because he is very much determined, he will carry it out this time. (原因)

　　比較：He is very much determined. He will carry it out this time.

　　2.使用分詞結構句。

　　The weather being fine, a large number of people went sightseeing.

　　比較：The weather is fine. A large number of people went sightseeing.

　　Africa is the second largest continent, its size being about three times that of China.

　　比較：Africa is the second largest continent. Its size is about three times that of China.

　　3.使用不定式句。

　　To be or not to be, that is a question. (莎士比亞)

　　To study or not to study, that is much different.(引申)

　　To do it well, you must plan it well.

　　比較：You want to do it well. And you must plan it well.

　　4.倒裝句

　　Only when we fully recognize its importance can we have control of its essence.

　　比較：After we fully recognize its importance, we can have control of its essence.

　　No sooner had he arrived home than it began to rain.

　　比較：He arrived home. And it began to rain.

　　5.失衡句

　　whether or not he will come is still unknown to all the people present.

　　比較：No one present knows whether he will come or not.

　　That he has done it all by himself is known to everyone.

　　比較：Everyone knows that he has done it all by himself.

　　當然，句子并不是越長越好，也不是越復雜水平就越高。凡事皆有度。太多長句的堆砌讓人覺得是買弄。有時侯，一個短小精辟的句子可以起到畫龍點睛的作用。特別是在文末段尾。比如：

　　●As a creature, every one knows.

　　●Actions speak louder than words.

　　●Practice makes perfect.