work at 努力做某事

　　They think I work at Starbucks. 他们以为我在星巴克工作。

　　How long did you work at the store? 你在这家店里工作了多久？

　　I worked at getting the job done. 我用心完成了这项工作。

　　I tried my best to work at this marriage. 这段婚姻我用尽了全力。

　　Learning English can be very difficult.  学英语是非常不容易的。

　　I know, but you have to work at it.  我知道，不过你必须得试试。