Answer: C, polyline
Question Answer Analysis:
Theoretically, the motion trajectory of the CNC machine tool is a polyline, that is, a polyline composed of straight segments.
In CNC machines, the trajectory of the tool depends on the machining program written.
Generally speaking, if the tool motion trajectory written in the machining program is a polyline, the CNC machine tool will move the tool in the direction of the polyline according to the programmed program to complete the corresponding machining operation.
It should be noted that in practical applications, due to factors such as machining errors, the motion trajectory of the tool may not be a completely accurate polyline, and there may be certain errors.
Therefore, when writing the machining program, it is necessary to carry out accurate calculation and control according to the specific situation to ensure that the motion trajectory of the tool meets the machining requirements.