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19.6 條件狀語從句
?
   連接詞主要有 if, unless, as/so long as, on condition that 等。.
   if 引導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. if  D. or
  答案A。 句意:除非你立即走,否則你就回遲到的?赊D化為 If you dong leave immediately, you will be late. B、D句意不對,or表轉折,句子如為 You leave immediately or you will be late.















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