1. The axis of the cone is _________.

x-axis
y- axis  
z-axis  
the line x+y+z = 0.

2. If 0, the origin, a fixed point and a variable point P moves along a fixed curve C, the surface generated by the line OP is _________.

cone
sphere
cylinder
a right circular cone. 

3. The surface generated by a line which passes through a fixed point and makes a constant angle with the fixed line through a fixed point is a _________.

cone
sphere
cylinder
a right circular cone. 

4. The semi vertical angle of the cone yz+zx+xy=0 is _________.

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