题目

参数方程(θ为参数)表示的曲线是( ) A.圆心在原点，半径为2的圆 Ｂ.圆心不在原点但半径是2的圆 Ｃ.不是圆 Ｄ.以上都有可能 答案：Ａ 解析:消去参数θ得普通方程是x2+y2=4，是以原点为圆心，半径为2的圆.(选出恰当的句子，补全对话) A. How clever!　　　　 B. Oh, I could. C. No, I couldn’t. D. What about you?　　　　 E. I learned it by myself. A: Could you look after yourself when you were four? B: (1) A: (2) Maybe I was more clever than you at that time. B: Don’t say that. Could you swim when you were four? A: Oh, no. (3) B: Of course, I could. A: Who taught you that? B: (4) A: Oh! You taught yourself swimming. (5) ndline