It is not long before they are so accustomed to swimming that they can pick up
weights from the floor of the pool.
请问,it is not long before ,里面,long before是一个词组吗,我查了,是很久以前的意思,这样加一个not,就成什么了,不是很久以前,
然后,如果不按一个词组算,把它拆开,这样翻,它不是很长,在适应游泳以前,
这到底是怎么回事,应该怎么理解