1. before long 的意思是“不久，很快”。（用于一般将来时或一般过去时）
I'll be back before long. 不久我就回来。（一般将来时）
Before long he got married. 不久他就结婚了。（一般过去时）
2. long before有两个用法：
1）很久以前 (单独使用，表示比过去某时早得多的时间。用于过去完成时)
She had left long before. 她老早就离开了。（过去完成时）
That had happened long before. 那事老早就发生了。（过去完成时）
【注】：
★ long ago 表示“很久以前”，指的是从现在算起的很久以前，通常与一般过去时连用：
I met him long ago. 我很久以前就认识他了。（一般过去时）
★ not long ago 表示“不久前”，指的是从现在算起的不久前，与一般过去时连用：
Not long ago a rare new species of bird-like dinosaur was discovered in
2）在……的很久以前，在还没有……的很久以前。如：
She had left long before his return [he returned]. （过去完成时）
在他回来的很久以前她就走了。
He had worked in the factory long before he got married. （过去完成时）
在他还没有结婚的很久以前他就在这家工厂工作了。
【注】：此时的主句谓语通常用过去完成时，但有时也可用一般过去时(因为 before 已体现了动作的先后关系)。如：
This happened long before you were born. 这事在你还没出生以前很久就发生了。
3. 区别以下句型：
1）It is [was, will be] long before… “在……前需要很久”，“费时间……才……”。
It was long before he came back. 过了好久他才回来。
It was long before we knew what was wrong with our plan.
费了很长时间我们才知道计划错在哪里。
2）It is / was not (won't be) long before… “不久就……”
It won't be long before you get well.
你不久就会康复的。（注意在before从句里用一般现在时代替将来时）
It won't be long before we see each other.
不久我们又会见面的。（注意在before从句里用一般现在时代替将来时）
练习：
1. They ______ on the earth tens of thousands of years ago, ______ humans came into being and their future seemed secure at that time.
A. had lived; long before B. had lived; long ago
C. lived; long before D. lived; before long
2. ______he will return to his native land.
A. It is long before that B. It is before long that
C. It won't be long before D. It will be long before
3. ______he returns to his native land.
A. It is long before that B. It is before long that
C. It won't be long before D. It will be long before that
4. ______he returns to his native land.
A. It is long before that B. It is before long that
C. It won't be long before that D. It will be long before
答案：1. C 2. B 3. C 4. D
