zài
1
(located) at
2
(to be) in
3
to exist
4
in the middle of doing sth
5
(indicating an action in progress)
他不家。
He is not at home.
办公室。
I'm at the office.
玩游戏。
I'm playing a game.
你的哥哥哪里工作
Where does your elder brother work?
医院工作,是个医生。
He works at a hospital, (he's) a doctor.