问题
选择题
平面上不重合的两点确定一条直线，不同三点最多可确定3条直线，若平面上不同的n个点最多可确定21条直线，则n的值为 [ ]
A.5
B.6
C.7
D.8
答案
答案：C
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平面上不重合的两点确定一条直线，不同三点最多可确定3条直线，若平面上不同的n个点最多可确定21条直线，则n的值为 [ ]
A.5
B.6
C.7
D.8
答案：C
| 补全对话。 | |
| Yang Mei: Hi, Lora! 1 Lora: Oh, I' ve been to many places, such as Xi' an, Hangzhou, Shanghai, Guilin and Tibet. Yang Mei: 2 Lora: Really? What places have you been to? Yang Mei: Very few. I've only been to Pingyao. Lora: 3 Yang Mei: It's in Shanxi. It's a small place, but it has a long history. It's one of the oldest towns in China. There you can see a well-kept city wall. Lora: 4 I've just seen a lot of natural beauties, but not much old Chinese culture (文化) yet. Yang Mei: 5
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