英语长难句令很多考生都头疼的一部分，但是其实英语长难句本身并不难，只是因为出题者在简单句上扩充，形成了一个生词多、句子长、结构复杂的句子。要想分析长难句本身，首先要找到句子主干，再看其他分支具体是做什么成分，这样就要求考生们具有一定的语法知识，才能很好的分析出这些句子成分。因此，考研英语老师为大家讲解考研中常见的英语语法。
独立主格结构由名词或代词加上其他成分(分词、不定式、名词、代词、形容词、副词或介词短语)构成。
独立主格结构没有主语和谓语，所以在语法上不是句子。但多有名词或代词表示的逻辑主语，分词或不定式表示的逻辑谓语，有时还有其他修饰成分。(判断一个结构是否是句子的标准就是看看这个结构是否有谓语动词。)这种结构通常在句子中起方式、时间、原因、条件等状语或状语从句的作用，主要用于书面语。使用动词非谓语形式的独立主格结构可以改为句子形式(从句):独立主格结构加上连词，非谓语动词改为谓语动词形式，这样就成为从句了。
例如:
Today being Sunday,the library isn't open.今天星期天，图书馆不开放。
(原因)改为从句:
As(Since)today is Sunday,the library isn't open.
例如:
There being no buses，we had to take a taxi.没有汽车了，我们只好坐出租车了。
Because there were no buses,we had to take a taxi.
The signal given，the bus started.信号发出后，公共汽车就启动了。
(时间)改为从句:
After the signal was given,the bus started.
The boy followed that man here，and climbed in，sword in hand.少年跟那个人到这里，并爬了进来，手里拿着剑。
The boy followed that man here，and climbed in，and had a sword in his hand.
The mid-term examination is over,the end-of-term examination to come two months later.期中考试结束了，两个月之后进行期末考试.
The mid-term examination is over,and the end-of-term examination is to come two months later.
Weather permitting,we'11 visit the Great Wall.如果天气允许的话，我们就去参观长城。
If weather permits,we'11 visit the Great Wall.
The boy followed that man here,and climbed in,sword in hand.少年跟那个人到这里，并爬了进来，手里拿着剑。(伴随状语)
上文例句中sword in hand是由“名词+介词短语”构成，表示伴随的情况。这种表示伴随情的独立主格结构，有时可以用with引出，二者的意思是一样的，with结构更加口语话，更加常用。
She left the office with tears in her eyes.她眼里含着泪水，离开了办公室。
The teacher walked into the classroom,with a ruler under his arm and some books in his hand.老师胳膊底下挟着一把尺子，手里拿着几本书，走进了教室。
The teacher walked into the classroom.He was holding a ruler under his arm and some books in his hand.
Tian'anmen Square looks magnificent with all the lights on.华灯齐放，天安门广场显得美丽动人。
With the boy leading the way,we found his house with no difficulty.由这孩子领路，我们毫不费劲地找到他的家。
With him to give us a lead,our team is bound to turn out well.有他给我们带头，我们队一定能搞好。
