Answer: D
Answer analysis: The core of automatic machining of machine tools is the numerical control system.
The numerical control system is a key component of controlling the automatic processing of machine tools, which can control the movement, speed, position and processing process of the machine tool according to the processing program to achieve high-precision and efficient processing.
The servo system is a part of the numerical control system, which is responsible for controlling the movement and position of the machine tool, but it is not the core of the automatic processing of the entire machine tool.
The machine tool body is the physical structure of the machine tool, including the bed, table, spindle and other parts, it is the main part of the machine tool, but it is not the core of automatic processing of the machine tool. The feedback device is used to detect the actual movement and position of the machine tool and feedback it to the numerical control system to achieve the control of machining accuracy, but it is not the core of the automatic processing of the entire machine tool.
Therefore, the answer is (D) CNC system.