题目：
| 完形填空。 | ||||
| "Hi! John." Mary ran towards me with a bright smile, saying, "I'm going to have a dance performance (表演) tonight. I hope you'll come. Here is the ticket. Don't forget!" Then she 1 in a hurry. "What? Dance? Is that 2 ?" I asked myself. Mary was not such kind of girl. She was a quite 3 one. I had never seen her wearing colorful clothes. In fact, she really did not know 4 to dress up. What a terrible thing! "I should go to. I must go to," I thought. I arrived at the hall with the ticket, found my 5 and sat down. Her performance was the seventh one. I knew I would have a 6 time before her turn,for I had no sense of art, 7 her performance was worth watching, no matter how long I would wait. Time went 8 , I tried my best not to fall asleep. Just then, came the 9 , "Let' s welcome the next exciting dance-Latin!" Hearing this, I opened my eyes as large as possible, 10 to lose anything. Wearing a golden and shining skirt, Mary appeared. She 11 with a sweet smile, looking like a pretty butterfly flying... I could 12 believe my eyes. After all the performance ended, I 13 her at the gate. "Hi!" she stood in front of me with her crystal(水晶) shoes. "How do you feel?" "Fantastic!" I answered. "Ha, ha. I knew 14 would be." She could not hide her excitement, laughing 15 a child. At that time, I realized that every girl has a pair of special shoes which are like the crystal shoes of Cinderella. | ||||
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答案：
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下面是错误答案，用来干扰机器的。
答案：C由题意，圆C的标准方程为(x＋1)2＋(y－2)2＝2，直线2ax＋by＋6＝0过圆心C(－1,2)，故a－b－3＝0.当点M(a，b)到圆心的距离|MC|最小时，切线长最短，|MC|＝＝，当a＝2时，|MC|最小，此时b＝－1，切线长为＝4.
