英语句型看似复杂多变，其实源于两大钻石句型，即主谓宾（本句型总共有4种形式，分别因谓语动词的不同特点而决定谓语之后有无宾语或补足语，具体为：主语+谓语、主语+谓语+宾语、主语+谓语+间接宾语+直接宾语、主语+谓语+宾语+宾语补足语，为了简明扼要的说明问题，本部分将其总结为一种句型“主语+谓语+宾语”）、主系表。
每一成分皆可复杂化，由此加大了句子的理解难度。下面就演示一下这两大基本句型是如何扩展成复杂的长难句的。
钻石句型：
①主语+谓语+宾语（S+V+O）
②主语+系动词+表语(S+V+P)
一、句子扩展：修饰成分加长
（一）钻石句型①主谓宾句型
The boy (主语) likes (谓语) English (宾语).
1.主语扩展：
The clever boy likes English.
The boy with a book in his hand likes English.
The boy who is full of imagination likes English.
The clever boy who is full of imagination with a book in his hand likes English.
注：主语中心词为the boy, 可以通过加形容词、介词短语、定语从句及其组合等成分使主语复杂化，从而增加理解难度。考研翻译中的主语考点多为修饰成分繁多的主语。
2.谓语扩展：
The boy likes English very much.
The boy likes English out of interest.
The boy likes English influenced by his parents.
The boy likes English, hoping that one day he can go abroad.
The boy liked English when he was five years old.
注：谓语动词like通过添加副词短语、介词短语、现在分词短语、过去分词短语、状语从句等进行扩展，从而使句子变得复杂，增加了理解难度。考研翻译中注意找准动词及其修饰成分,以弄清逻辑关系。
3.宾语扩展：
The boy likes American English.
The boy likes English, the international language.
The boy likes English which is the most widely spoken language in the world.
The boy likes English spoken by many people nowadays.
The boy likes English, a beautiful language, spoken by many people living in every corner of the world.
注：宾语English通过添加形容词（短语）、同位语、定语从句、分词短语及其组合进行扩展，从而使简单句变得复杂化。考研翻译中要注意这些修饰成分，如分词结构要找出逻辑主语等，定语从句要找出先行词，等等。
（二）钻石句型②主系表句型
The girl (主语) is (系动词) Mary (表语).
各部分扩展：
The girl in a pink hat with a book in her hand is probably Mary a kind-hearted girl of inexhaustible energy which often amazes her classmates.
注：此句的扩展同上（也是通过添加修饰成分变复杂），不再赘述。
二、句子扩展：成分替换
句子的复杂不仅体现在修饰成分繁多上，还体现在句子成分本身的复杂化上，下面就通过句子成分由简单到复杂的替换来演示句子是如何变难的。
（一）钻石句型①主谓宾句型
主语扩展：
The event amazed the world.
What happened on July 15, 2001 amazed the world.
To hold the 2008 Olympics in China amazes the world.
Holding the 2008 Olympics in China amazed the world.
That China is to hold the 2008 Olympics amazes the world.
注：由此可见，充当主语的除了简单的名词(短语)、代词、数词，还可以是形式比较复杂的动词不定式(短语)、动名词(短语)、主语从句。考研翻译中明确这一点，才能打开思路，更好地划分句子成分，从而做到真正理解句意，进而很好的用汉语表达出来。
宾语扩展：
He can hear me.
He can hear the strange sound.
He can hear anything happening in the building.
He can hear the sound from that building.
He can hear a girl crying in the building.
He can hear whatever happens in the building.
He decided to check what’s going on in the building.
He considered going to the building for a look.
注：由此可见，充当宾语的除了简单的名词(短语)、代词、数词，还有形式比较复杂的动词不定式(短语)，动名词(短语)，宾语从句。同样的，考研翻译中明确这一点也非常重要，有助于打开思路，理清句子成分。
（二）钻石句型②主系表句型
主语扩展：钻石句型①中的主语扩展（成分替换）已经很明确了，此处不再重复。
表语扩展：
They are beautiful.
They are in the zoo.
They are beautiful animals in the zoo.
They are interested in the new invention.
To see is to believe.
That is what we are talking about.
注：由此可见，充当表语的成分繁多，有形容词(短语)，介词短语，动词不定式(短语)，分词(短语)，名词，表语从句。考研翻译中若这些充当表语的成分变得更长一些，要注意识别。
三、示例
通过下面这个例子，并结合以上句子的扩展，体验一下英文句子的各个成分及结构。
But science does provide us with the best available guide to the future, and it is critical that our nation and the world base important policies on the best judgments that science can provide concerning the future consequences of present actions.
解析：
并列句。第一个分句主干：science does provide us。其中with the best available guide to the future为状语修饰provide， the best available和to the future分别为guide的前置定语和后置定语，由此本句宾语被复杂化： 第二个分句主干：it is critical that...,其中，it为形式主语，that从句为真正的主语，从句主语为名词短语our nation and the world, base...on...为固定搭配，第二个that从句为judgments的定语从句，分词结构concerning...为judgments的后置定语。
