高二英语语法题~求详解,关于 since after before的区别等..

高二英语语法题~求详解,关于 since after before的区别等..
The experts pointed out that it would be many years ______ the survivors of the earthquake get fully recovered.
A,after B.unless C.since D,before

四个句型五个例句：
句型1.it was 时间点 when sth.happned.
句意：当某事发生时,时间是XXX.
例1：It was 1997 when Hongkong returned to China.
句子分析：主句--it was 时间点.
其中：it 是主语（不是形式主语）,指代时间.（例如：
It is six o'clock now.
It was ten o'clock when I got home.)
when-从句为 时间状语从句,也可以放在主句前面：
When sth.happened,it was XXX.
句型2.it was 时间段 before sth.happened.
句意：（在某件事情发生之后,）另一件事情发生之前,这段时间是...
翻译1.过了...,就发生了另一件事.(主观认为时间较短）
翻译2.过了...,才发生另一件事.（主观认为时间较长）
例2：It was 2 years before Macow returned to China too.过了两年澳门也回归中国了.
析：这句话有例1为前提,it指的是1997年之后、1999年之前这一段时间的长度(two years.)
误：It was two years after .,两年后,...也...了.
补充：before的前提是：前面发生过一件事,从这个时间开始,到另一件事情发生之前(before) 这一段的时间（时间段）是多长.
如果这个时间段长或不长,有两种不同的译法.
1.才过了多久就...了.
其中最常见的一个例句就是：It wasn't long before sth.happened.不久就...了.
2.过了很久才...
时间的长短是一相对的概念.
二年时间相对百年的殖民时代是短的,所以可以译作：才过了两年澳门也回归了.
但如有人考了两年才考出驾照.
He began to learn how to drive a car in 2005.
（It was 2005 when he began to learn how two drive a car.)
It was two years before he got the drive licence.就得译作：过了两年才领到驾照.
句型3.it is (=has been) 时间段 since sth.happened.
句意：自从某事发生以来（到现在为止）时间已经是多久了.
例3：It is (= has been ) 15 years since Hongkong returned to China.香港回归中国已经有15年了.
注：本来就是现在完成时has been 与since 从句连用.现代英语用is代has been了.
句型4：强调句型：it is(/was)+被强调的句子成分（主语、宾语或状语）+that+剩余的句子成分
例4：It was in 1997 that Hongkong returned to China.香港是在1997年回归中国的.
去掉结构词,原句子为：Hongkong returned to China in 1997.
请注意例1和例4的细微差别.
例5：before 句型的另一个时间,将来时态：it will be 时间段before sth.happens
例：It will be N years before XX returns to China.
数轴示意：
|.> Time
1997 1999 now future
The experts pointed out that it would be many years ______ the survivors of the earthquake get fully recovered.
A.after B.unless C.since D.before
答：D
译：专家们指出,要过许多年之后那些地震的幸存者才能完本恢复（指心灵上的创伤）.
析：本题是最后一个例句在间接引语中的运用.
常见错误是A.因为汉语翻译中有：...之后.many years after 正好合意!BC容易排除.