They replaced trams by buses.是什么意思？

They replaced trams by buses.

他们用公共汽车代替了电车.

they

pron. 他/她/它们，人们，大家，政府，当局，她们；

例句
The storms had abated by the time they rounded Cape Horn.
他们绕过合恩角时，暴风雨已经减弱。

replaced

v. 取代( replace的过去式和过去分词 )，更换，把…放回原位，（用…）替换；

例句
The mist had been replaced by a kind of haze that seemed to amplify the heat...
薄雾散了，取而代之的是一种似乎更添酷热的烟霭。

trams

n. 有轨电车( tram的名词复数 )；

例句
The trams carried an average of 279 200 boardings daily in 1997.
年内,电车载客量平均每日279200人次.

by

prep. 在…旁边，表示方式，由于，经过；adv. 经过，表示保留或保存时用，短暂拜访；

例句
...expensive make-up that we saw being advertised by a beautiful model...
我们所见的由一位漂亮模特代言的昂贵化妆品

buses

n. 公共汽车；

例句
One armoured column attempted to blast a path through a barricade of buses and trucks.
一个武装纵队试图从公交车和卡车组成的路障中间炸出一条通道来。