根据语境，填人适当的词或句子，补全对话 。
A: Look! What's that under the tree?
B: 1 _ Oh, it's a backpack.
A: Who does the backpack belong to?
B: 2 Let's open it. Look here! It might be a girl's 3 _ there is a red T-shirt.
A: Well, it 4 a boy's. The red T-shirt might be a present for his sister.
B: Hey, I know whose backpack it is.
A: Really? Who is the _ 5 _ of it?
B: It must be Pierre's. The T-shirt has his name on it.
