He knew it was useless to protest.

　　他知道抗議是徒勞的。

　　I was conned into buying a useless car.

　　我上當受騙買了輛不能用的汽車。

　　I'm useless at French.

　　我的法語不太行。

　　It is useless to speculate why he did it.

　　對他為什么這么做妄加猜測毫無用處。

　　The measures were decried as useless.

　　這些措施受到指責，說是不起作用。