off the top of one's head直译过来就是：“不在某人的头顶”，这个短语的正确意思是：“没有经过仔细考虑或仔细计算”。因此，当美国人说"I can't tell you the information off the top of my head."时，他/她要表达的意思就是:"I can't tell you the exact information because I don't know whether the news is true or not."、"I can't tell you the information because I can't make it for sure right now."。
Terry: Someone says that we will be sent to Japan for business next Friday, and we will stay there for a week. I s that true?
Benjamin: I can't tell you the information off the top of my head. I'll have to check it.
①The boss will come to inspect our work, right?
②Will our boss come back from the business next week?
③When will the negotiation be held?
④It is said that the opening ceremony will be held in two days.
ceremony n. 仪式
I have to say that this opening ceremony was the most impressive I have EVER seen.
There are many people who should be thanked today, as it is due to their hard work and dedication that this graduation ceremony is possible.
Among all societies legal marriage is usually accompanied by some kind of ceremony that expresses group approval of the union.