futile的名詞形式是什么

　　例句：

　　It would be futile to protest.

　　抗議也無(wú)用。

　　It would be futile to argue with him.

　　跟他爭(zhēng)辯是徒勞的。

　　There is no point in continuing this futile fight!

　　持續(xù)這場(chǎng)無(wú)效的戰(zhàn)斗沒(méi)有意義！