I didn't expect her to have started working yet, but she was already (hard) at it when I arrived. [=she was already working (hard) when I arrived]我本来没指望她开始工作，但我到的时候她已经在（努力）干活了。

My neighbors are always arguing, and they were at it again last night. [=they were arguing again last night]我的邻居总是吵架，昨晚他们又吵起来了。

Since we're cleaning the kitchen, we should wash the floor while we're at it. [=we should wash the floor when we clean the kitchen]既然要打扫厨房，我们应该同时把地板也擦了。

“I'm going to the store to buy a newspaper.” “While you're at it, could you get some milk?”“我要去商店买份报纸。”“你买报纸时，顺便买点牛奶好吗？”