方位介词 in, on, under — 英语情景题

情景对话：Tom 和 Lily 在教室里整理书包和课桌。请从 in, on, under 中选择正确的介词填空，将对话补充完整。 Tom: Lily, where is my ruler? Lily: Look! It's (1)________ your pencil case. Tom: Oh, yes! Thank you. And where is my English book? Lily: It's (2)________ the desk. Tom: I see it. Is my ball under the chair? Lily: No, it isn't. Your ball is (3)________ the box. Tom: Thanks, Lily!