提示：戴维打电话找布鲁斯，戴维想询问布鲁斯有关中国古钱币的问题，布鲁斯不在家，李接了电话。
Mrs Lee: Hello. 68178502.
David : Hello. 51 ?
Mrs Lee: Sorry. 52 . Can I take a message?
David: Yes. This is David, Bruce's friend. I want to ask him for some Chinese ancient coins. He told me he had got some recently. 53 I don't care if they were made of different metals. I just want to add some more coins in my collection.
Mrs Lee: OK. "I'll tell him. Would you like him to ring you back later?
David : Well, I won't be at home later this day. Would you please ask him to ring me tomorrow morning?
Mrs Lee : Sure. 54 ?
David: Oh, sorry. 55 The new number is 66129853.
Mrs Lee: OK. I'll write a message for him.
David: It's really nice of you, Madam. Thank you very much. Goodbye!
Mrs Lee : Bye !
根据以上内容,回答题
第51题应填入_____