题目

完形填空 Many Americans like to have their vacation in   1   countries. One day an American    2   comes to visit China. This is her first time (次数) to China and she   3  to make some friends there. She meets a Chinese. This Chinese wants to talk    4    with the American. When he sees her, he comes up, says “    5    ” to her, then he begins his first talk with a person    6    an English-speaking（说英语的） country.“How old are you?” the Chinese    7  . “I’m    8  . Please don’t ask a lady (女士) about her   9   .” an如图1，两半径为r的等圆⊙O1和⊙O2相交于M，N两点，且⊙O2过点O1．过M点作直线AB垂直于MN，分别交⊙O1和⊙O2于A，B两点，连接NA，NB．（1）猜想点O2与⊙O1有什么位置关系，并给出证明；（2）猜想△NAB的形状，并给出证明；（3）如图2，若过M的点所在的直线AB不垂直于MN，且点A，B在点M的两侧，那么（2）中的结论是否成立，若成立请给出证明．