sb was doing sth at some的意思

sb was doing sth at some的意思
sb was doing sth at some的意思

sb was doing sth at some的意思
某人在某时做某事(过去进行时)表示在过去的某一时段这人正在做某事.

don't know

什么呀 那是 be good at
不过原题里的“at some”好像也有点问题吧
真没见过