We need a clear understanding of the problems involved.

　　我們需要了解清楚所涉及的各種問題。

　　This research has done much to advance our understanding of language learning.

　　這項(xiàng)研究大大提高了我們對(duì)語言學(xué)習(xí)的認(rèn)識(shí)。

　　Stop fussing around and find something useful to do!

　　別瞎忙活了，找點(diǎn)有用的事干！

　　Your local library will be a useful source of information.

　　你們當(dāng)?shù)氐膱D書館就是很好的資料來源。

　　It's a useful introduction to an extremely complex subject.

　　這是對(duì)一門極為復(fù)雜的學(xué)科的有益入門教程。