before，after，until的用法与区别?

before 在...以前 after 在...以后 until 直到 before的用法： 1． before用作连词时，意思是“在……之前；还没来得及 …… 就”。例如： Before she could move, she heard a great noise, which grew to a terrible roar. 她还没来得及动弹，就听见有很响的声音，接着就成了可怕的隆隆轰鸣声。 Before I could sa