20. Sara: Hi! I want to mail this box of books to Japan.
Clerk: Sure. But there’s a weight limit of five kilograms, and that box looks big.
Sara: Oh, _______________
Clerk: Let’s see...yes, four kilograms even.
(A) you forgot to write the return address.
(B) I'd like to send it by registered airmail.
(C) your small packets are good for airmail.
(D) I think it weighs less than five kilograms.