最大的一位数是____，最小的两位数是____，它们相差____。最小的三位数是____，最大的两位数是____，它们的差是____。

下列关于学习方式和学习方法正确的说法是   （   ）

    Mr. and Mrs. Brown lived in a small town near London with their children. Sometimes Mr. Brown came back home from work very late, when his wife and the children were asleep, and then he opened the front door of this house with his key and came in very quietly. But one night when he was coming home very late, he lost his key, so when he reached his house, he rang the bell. Nothing happened. He rang it again. Again nothing happened. Nobody moved inside the house. Mr. Brown knocked at(敲)the bedroom window, he spoke to his wife, he shouted, but she didn't wake up. At last he stopped and thought for a moment. Then he began to speak like a small child. "Mother! "he said. "I want to go to the toilet!" He spoke quite quietly but at once Mrs. Brown woke up. Then he spoke to her, and she opened the door for him.

北京奥运会开幕的时间是____。