史学家为了便于研究东周时期的这段历史，将之划分为哪两个时期（    ）

（Ⅰ）求椭圆C的方程；

（Ⅱ）过点（0，t）作圆O的一条切线交椭圆C于M，N两点，求△OMN的面积的最大值．

根据对话内容，从方框内的选项中选出能填入空白处的最佳选项，选项中有两项为多余选项。
Mrs. Lee: Hello. 68178502.
David:  Hello.____  ?
Mrs. Lee: Sorry.____ . 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. ____  . 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.____ ?
David:   Oh, sorry.____   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!

把横线上的数改写成用“亿”作单位的数．按顺序填写，分别是____，____，____。