Which port is commonly used for digital connection between a computer and an external device?

Correct answer: USB port

The USB port is the best general answer because Universal Serial Bus is designed to connect computers with many digital peripherals, including keyboards, mice, printers, cameras, and storage devices. An audio port is mainly intended for sound signals, a video port for display signals, and a power socket supplies electricity rather than carrying ordinary peripheral data. Thus option D is the broadest and most suitable choice.