这两个词放在句首或句尾在用法上是一样的,只是族在句首,就是两个句子,放在句中,就是一个句子,也就是说是用if或unless将两个句子连接成一个句子.
例:If it were not for your help,I would not have succeeded.要不是你的帮忙,我是不会成功的.
= I would not have succeeded if it were not for your help.
unless = if.not用来引导否定的条件句,也就是说用来代替否定的if从句.
例:If Max doesn't come on time,we will leave without him.如果Max没准时来,我们就不等他先走.
=Unless Max comes on time,we will leave without him.
not+unless=only...if 表示"如果...的话"
例:Venus won't come unless Nancy does.Venus不会来,除非Nancy有来.
=Venus will not oonly come if Nancy does.
注意,这里的only只是用来强调if ,与 if only(要是...就好了) 意思不同喔~
