句子多样性
单调的句式和结构、长度相近的句子使作文呆板单调，缺乏生动性和说服力;而灵活多变的句子样式和结构则使作文语言生动，自然流畅，丰富多彩。具体包括以下几个方面：
长短句变换：简单句、并列句和复合句交替运用。长句准确生动，长于说明推理;短句简洁明快，意义明确，印象深刻，描述动作，表明主旨，总结归纳，非短句不可。既然各有所长，在写作时应根据实际需要，交替使用简单句、并列句和复合句，以达到“段间长短不一，全篇句式万千”、丰富多样的效果，给读者以及阅卷老师以永恒的新鲜感。
结构多样化：我们学过非谓语动词结构(包括不定式结构和分词结构)、无动词结构、分隔结构、比较结构、独立结构、with复合结构、特殊否定结构、it结构、平行结构、强调结构、倒装结构，等等。其中最为神通广大的是非谓语动词结构，在句中或作主语、宾语，或作表语、宾语补足语，或作定语修饰名词，或作状语表示条件、原因、让步、时间、方式、目的、结果、伴随状况等，不一而足。
非谓语动词结构可以简化大部分英语从句，产生语言简练、结构丰富多样的效果，请看下列转化实例：
名词从句可转化为非谓语动词结构
1. That John won the marathon surprised us.
John’s winning the Marathon surprised us.
2. I have not decided whether I should vote for Clint.
I have not decided whether to vote for Clint.
定语从句可转化为非谓语动词结构
1. The man (who is) standing at the gate is my English teacher.
2. The car (that was) repaired yesterday by him is my mother’s.
3. The next train that arrives is from New York.
状语从句可转化为非谓语动词结构
1. After he had watered the garden, he began to mow the lawn.
Having watered the garden, he began to mow the lawn.
2. When they are heated metals expand.
(When) Heated, metals expand.
3. Because I do not know what to do next, I want to ask for your advice.
Not knowing what to do next, I want to ask for your advice.
4. I spoke slowly and clearly in order that the audience could understand me.
…in order for the audience to understand me.
5. If we are united, we stand; if we are divided, we fail.
United, we stand; divided, we fail.
6. Though he has lived in Canada for tree years, he still cannot speak English well.
Having lived in Canada for three years, he still cannot speak English well.
当然，要掌握丰富多样的词汇和句型变换技巧，就要能够掌握一定量的词汇和句型，这样才能在托福写作中大放异彩。
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