Answer: (D) RS-232
Question Answer Analysis:
The RS-232 port of the numerical control system is connected to an external computer and can send or receive programs.
In CNC machine tool control technology and systems, the RS-232C port of the CNC system can be connected to an external computer for sending or receiving programs.
The RS-232C port is a standard interface for numerical control systems that can be connected to an external computer via a serial communication line.
Through the RS-232C port, numerical control systems and external computers can realize data exchange and program transmission.