【单选题】
利用在平面上取点，直线的作图，可以解决以下（）（）（）三类问题。
①
可以确定平面上的坐标点；完成已知平面上的点和直线的投影；完成多边形的投影
②
判断已知点、线是否属于已知平面；完成已知平面上的点和直线的投影；完成多边形的投影
【单选题】
当直线、平面与投影面平行时，该投影面上的投影具有( )
①
Normal
0
7.8 磅
0
2
false
false
false
EN-US
ZH-CN
X-NONE
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积聚性
②
Normal
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7.8 磅
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EN-US
ZH-CN
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真实性
③
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类似收缩性
④
Normal
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7.8 磅
0
2
false
false
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ZH-CN
X-NONE
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收缩性