许多词既可作介词又可作副词：
He got off the bus at the corner.(介词)
他在拐角处下了公共汽车。
He get off at the corner.(副词)
他在拐角处下车。
这些既可作介词又可作副词的词中最重要的有above，about，
across，along，before，behind，below，besides，by，down，in，near，off，on，over，past，round，since，through，under，up：
They were here before six.(介词)
他们6点之前在这里。
He has done this sort of work before.(副词)
他以前干过这种工作。
Peter is behind us.(介词)
彼得在我们的后面。
Hes a long way behind.(副词)
他远远地落在后面。
She climbed over the wall.(介词)
她爬过墙头。
Youll have to climb over too.(副词)
你也得爬过去。
When the meeting was over the delegates went home.(副词)
会议结束后代表们各自回家了。(这里over=finished结束)
The shop is just round the corner.(介词)
商店拐过街口就是。
Come round(to my house)any evening.(副词)
晚上有空来我家串门。
He ran up the stairs.(介词)
他跑上楼梯。
He went up in the lift.(副词)
他乘电梯上去了。
这些词中许多可以用来构成短语动词：
The plane took off.
飞机起飞了。(离开了地面)
He came round.
他恢复知觉了。(恢复了意识)