連接詞主要有 if, unless, as/so long as, on condition that 等。.

if 引導(dǎo)的條件句有真實條件句和非真實條件句兩種。非真實條件句已在虛擬語氣中闡述。

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.

典型例題

You will be late ___ you leave immediately.

A. unless B. until C. ifD. or

答案A。 句意：除非你立即走，否則你就回遲到的。可轉(zhuǎn)化為 If you dong leave immediately, you will be late.B、D句意不對，or表轉(zhuǎn)折，句子如為 You leave immediately or you will be late.