The soldiers all used to do a six-month tour of duty in Northern Ireland.
士兵過(guò)去都要在北愛(ài)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(guò)，記得嗎？
Potential energy can be used to do work.
勢(shì)能可以用來(lái)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。