核心词汇运用 — 英语填空题

看提示词，用其正确的物主代词形式填空。Sarah has a lovely dog. That dog is ___ (she). The students are cleaning the playground, so it is ___ (they) duty. I found a key on the desk. It isn't ___ (my). Mike and John share a big room, and the room is ___ (their).