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月。
I used to do that when you were a little girl, remember?
在你還是小女孩的時候我曾經那麼做過，記得嗎？
Potential energy can be used to do work.
勢能可以用來做功。
The lecturer used to do well, but he seems to have gone off now.
這個講師以前挺好，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。