“拉伸”命令沿Z轴或指定的拉伸路径，将封闭的二维多段线、样条曲线、以及多边形、圆、椭圆和面域拉伸指定的高度，以生成三维实体模型。

A. 直线、圆和圆弧

B. 椭圆和椭圆弧

C. 多段线

D. 样条曲线

A、封闭的多条的

B、开放的多条的

C、封闭的多条的

D、封闭的一条的

简述样条曲线命令的操作过程

1.Bzier曲线与B样条曲线有何联系？Bezier曲线在何种情况下可以变为B样条曲线？ 2.实体模型的计算机内部表示方法主要有哪些？各有何特点？ 3.实体模型的建模方法有哪些？ 4.以下IGES文件是由哪个软件生成？共表示了几个几何元素？分别是什么？写出其中表示曲线参数的数值。 IGES file generated by CAXA EB 2001 for windows S 1 1H,,1H;,,38HC:\Users\ylcai\Desktop\工程图文档1.igs,38HCAXA Electronic BoG 1 ard 2001 for Windows,3H1.0,32,38,6,308,15,34HC:\Users\ylcai\Desktop\工程G 2 图文档1,1.,2,2HMM,20000,200.,13H200401.092918,0.0001,226.8381999623,,,9,G 3 0,13H200401.092918; G 4 110 1 0 1 0 0 0 000000000D 1 110 70 8 1 0 D 2 100 2 0 1 0 0 0 000000000D 3 100 70 8 2 0 D 4 126 4 0 1 0 0 0 000000000D 5 126 70 8 6 0 D 6 110,-204.0960591133,-31.2727832512,0.0,0.0,0.0,0.0; 1P 1 100,0.0,-204.0960591133,-31.2727832512,-181.3539182643, 3P 2 -31.2727832512,-181.3539182643,-31.2727832512; 3P 3 126,6,3,0,0,1,0,0.0,0.0,0.0,0.0,0.4323454846,0.6258006671, 5P 4 0.8786478802,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,-204.0960591133, 5P 5 -31.2727832512,0.0,-183.4355638043,-4.2719744137,0.0, 5P 6 -129.5976494183,46.3559296776,0.0,-71.0802724517,-22.5151148477, 5P 7 0.0,-25.4797993785,40.2730869379,0.0,-4.4065542544,8.4644908599, 5P 8 0.0,0.0,0.0,0.0,0.0,1.,0.0,0.0,1.; 5P 9 S 1G 4D 6P 9 T 1

A、circle

B、linel

C、spline

D、scale