It is not long before they are so accustomed to swimming 这里的it is为什么在前面,是什么用法

not long before 和 before long有什么区别呢?It won't be long before we meet again.We will meet again befor long.这两句有区别吗？ It is hard the work befor supper It won`t be( )scientists can find out medicine to cure this disease.A.long after B.befor longC.long befor D.long since What is taken from you befor you get it?帮忙! it won't so long ,和it is not so long有何不同?都是什么意思? it is not long after 和it is not long before 意思都是不久的意思吧? the dress is not too long.It is not too large.(合并为一句) How long is it? It was not long until ... The snake is very long.It is not( )（ ）里填什么? It is not long before they are so accustomed to swimming that they can pick up weights from the floor of the pool.It is not long before not to know what happened befor one was born is always to be a chilld是什么 young short fat heavy old his bike is new.It is not ( )the box is light.It is not ( )mary is thin.she is not ( )the snake is very long.It is not ( ) it's a very big animal.it can not jump.it is heavy.it has two long teeeh.what am befor long shortly after如何区别? 9. ____ he will leave for Beijing. A. It will not long before B. It is before long that C. It is before long D. It was before long that答案是D选项.为什么不能选B选项 将下面两句合并为一句The dress is not too long.It is not too large. So long yes it is so long.