在...之前就... 强调主句动作先发生，从句动作后发生
You should wash your hands before you have lunch
.....才.... 强调从句谓语动作发生的太慢或太晚
He nearly knocked me down before he saw me
趁....还没发生/以免
We have to take effective measures before things get worse
没来得及.....就....目的在于强调从句动作发生之前，主句动作已经发生
He hung up before I could answer the phone
it was+时间段+before+一般过去时，过了多久....才...
It was a long time before I got to sleep again
it was not +时间段+before +一般过去时 没过多久，就.....
It wasn't long before he told me about this affair
it will be+时间段+before+一般现在时 要过多长时间才
It will be five years before we meet again
It will be not+时间+before+一般现在时 没过多长时间就.....
It won't three hours before he arrives at the nus stop.
在某日 某时 某事前
The war has a ended only a month or so before
在某地前方 某距离处
The station is on the right, one mile before downtown Romney
