COM 4 uses which I/O port? A. 2F8H B. 3F8H C. 3E8H D. 2E8H E. None of the above

The correct answer is: B. 3F8H

COM4 uses I/O port 3F8H. This is a standard I/O port for serial communication. It is used to send and receive data between the computer and a serial device, such as a modem or a printer.

The other options are incorrect. Option A, 2F8H, is the I/O port for COM2. Option C, 3E8H, is the I/O port for COM3. Option D, 2E8H, is not a valid I/O port.

I hope this helps!