Although it is midnight now,my father is still A.in work B.i

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