12.用于以if引导的虚拟条件从句

if引导的虚拟条件从句，如果省略if，就应将were，should，had和could等置于从句主语之前。(参见虚拟语气和状语从句)

Had I known that air conditioners cause so much pollution，I would never have bought one．(人教大纲版高二上第68页)

要是我以前知道空调能造成大量的污染，我就不会买它了。

Were she not busy in writing a book，she would have gone to the party．

若不是忙于写书，她早去参加聚会了。

Should the room be smaller，there would not be enough space for the shelf．

若是屋子再小一点，就没有地方放书架了。

Should you feel the urge to pack your bags and explore what the world has to offer，you might want to consider one of the destinations below．(人教大纲版高二下第35页)

如果你感到有迫切的愿望打点行装去探索世界，那么你可能会考虑下列目的地中的某一个。