Question

He had worked in this school ___ the war broke out，but___ he had to leave the school.

A long before；long befor
B before long；before long
C long before；before long
D before long；long before

Answer 1

1.before long 不久以后
2.long before 很早以前
画个草图，区别long before和before long，这样更容易理解。
<----long before---->||<---before long--->
-----------------------now----------------------future
很久以前---------------现在-------不久之后--->

before long 不久以后，很快
eg: They came back before long. 他们很快就回来了。
long before 很久以前
eg:I knew Tom long before I knew you. 我在认识你之前很久就认识了汤姆。
We had not waited long before she came. 我们没等多久她就来了。

答案选择C选项。
希望可以帮到你~~~

Answer 2

C