The soldiers all used to do a six-month tour of duty in Northern Ireland.

　　士兵過去都要在北愛爾蘭服役六個(gè)月。

　　I used to do that when you were a little girl, remember?

　　在你還是小女孩的時(shí)候我曾經(jīng)那么做過，記得嗎？

　　Potential energy can be used to do work.

　　勢(shì)能可以用來做功。

　　The lecturer used to do well, but he seems to have gone off now.

　　這個(gè)講師以前挺好，但如今似乎講得差了。

　　I used to do it all the time.

　　我以前都是這樣的。