形容詞 useless:

1. having no beneficial use or incapable of functioning usefully

1. It's useless to continue such a barren argument.
   繼續(xù)這種無聊的爭辯是無用的。
2. I had expended much time on the work but they told me it's useless.
   我花了很多時間在這件工作上，他們卻告訴我說這是無用的。
3. It's useless to argue with them.
   同他們爭論是沒有用的。