30.A: Dale, welcome to my room!
B: Wow, room is nice and tidy.
A: Thanks.
B: Is this a(n) ?
A: Yes, it is. This model plane is white. Look! Here is a yellow one.
B: is that in your bookcase?
A: It's a watch. But it's not .
B: Is it your brother's?
A: Yes.
B: the radio? Is it your brother's, too?
A: No, it's my sister's.