Where did the boy paint his pictures?

W: What are you doing, darling?
M: I’m looking at my pictures. I painted them in class.
W: Let me see. Oh, what’s this?
M: It’s a house.
W: And what are these?
M: They are rooms. This room is the kitchen, and this is my bedroom.
W: What about these green lines?
M: Mum, they are not lines. They are trees. These trees are in the blue sky.
W: Really? Then is this a plane?
M: It’s not a plane. It’s you, Mum. You’re flying in the sky.
W: Oh, really? That’s a strange picture.