雙語例句：
Stop fussing around and find something useful to do!
別瞎忙活了，找點有用的事幹！
Your local library will be a useful source of information.
你們當地的`圖書館就是很好的資料來源。
It's a useful introduction to an extremely complex subject.
這是對一門極為複雜的學科的有益入門教程。
It's useless to fire away with such trivial details.
喋喋不休地談這些瑣碎細節是無用的。
When it comes to getting things done, he's useless.
一涉及做事，他便不中用了。