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.