The relationship of AB and CD is ()
A. screw
B. intersect
C. parallel
D. virtical
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There are () limitation elements on a sylinder
A. 2
B. 4
C. 3
D. non
The side edges of a pyramid
A. Intersect in a vertest
B. parallel
C. screw
D. alignment
When a cylinder is cut by a plane which parallel with the axis ,the shape of the intersection line should be a
A. rectangle
B. circle
C. triangle
D. ellipse
Zig-zag line is used to discribe
A. broken -out
B. symertry line
C. axis
D. invisible line