全国大众英语测验语法——前提状语从句
连接词重要有 if, unless, as/so long as, on condition that等。.
if指导的前提句有真实前提句和非真实前提句两种。非真实前提句已在假造语气中论述。
unless = if not.
Let's go out for a walk unless you are too tired.
If you are not too tied, let's go out for a walk.
典范例题
You will be late ___ you leave immediately.
A. unless B. until C. ifD. or
谜底A。句意：除非你立刻走，不然你就回迟到的。可转化为 If you dong leave immediately, you will be late.B、D句意不对，or表转折，句子如为 You leave immediately or you will be late.
关键字：英语语法 状语从句 状语从句 让步状语从句 时候状语从句 前提状语从句