by bus 没有过去式,by bus 是介词,不是动词，乘公共汽车的意思。
例句
It is possible to get there by bus.
可以乘公共汽车到那里。
Itll work out cheaper to travel by bus.
算来还是乘公共汽车便宜些。
You\'d be better going by bus.
你坐公共汽车去会更好些。
He goes to work by bus.
他乘公共汽车去上班。
They had to travel everywhere by bus.
他们只得乘公共汽车出行。
