Where did the boy paint his picture?

W: What are you doing, dear?
M: I’ m looking at my picture, which I painted in class.
W: Let me see. Oh, what is it?
M: It’ s a house.
W: What about these green lines?
M: Mum, they are not lines. They are trees. These trees are growing in the blue sky.
W: Really? Then is this a plane flying in the sky?
M: No, Mum! It’ s you, not a plane! You’re flying in the sky, just beside these green trees.
W: Oh, really! What a strange picture!