用哪个都可以，主要取决于 it 指代什么。～如果 it 指代地板，应该是 A desk is on it.～如果 it 指代房间，应该是 A desk is in it.～如果 it 指代塌陷后的屋顶，应该是 A desk is under it.
请问 短文呢？
