Although it is midnight now,my father is still A.in work B.in the work C.at work D.at the work

Although it is midnight now,my father is still A.in work B.in the work C.at work D.at the work
应该选哪个?为什么?
第二题 完成句子
他们过去吸烟很凶,但是现在不吸了.
They a lot,but now they give it up 一个问号代表一个单词