by是什么时态的标志词

　　All the statistical computations were performed by the new software system.

　　所有的统计计算均由新的软件系统完成。

　　They won by a single goal after extra time.

　　他们在加时赛中仅踢进一球即获胜。

　　They've increased the price by 50%.

　　他们已经把价格提高了50%。

　　Now I can walk to work instead of going by car.

　　现在我可以步行去上班，而不必开车了。

　　I'm always broke by the end of the month.

　　我总是一到月底就没钱花了。