1、当先行词为all、anything、everything、nothing、something、few、little、much、any等不定代词时。2、当先行词被 all、any、little、no、few等词修饰时。3、当先行词为形容词最高级或被最高级修饰时。

例句：Keep going like that ─ you're doing fine.就这样做下去——你做得蛮不错嘛。You could see from his face that he was lying.从他的表情上你可以看出他在说假话。Had I known that I would never have come.要是早知道，我绝不会来的。