Which of the following statements about I/O address is true?

Which of the following statements about I/O address is true?

A.
An I/O address is a method of transferring information directly from a disk drive to a memory location.

B.
An I/O address is an event, which requires processor’s attention.

C.
An I/O address is the display adapter address on the CPU.

D.
An I/O address is a communication port between a device and the CPU.