Concept:The main difference lies in where each modem is installed and how it connects to the computer.
Explanation:An internal modem is an expansion card that is installed inside the computer case.
It fits directly into a PCI or ISA expansion slot on the motherboard.
Because it is inside, it draws power from the motherboard and needs no separate cables.
An external modem is a standalone device that remains outside the computer.
Traditionally, it connects to the computer through a serial port on the back of the system unit.
External modems have their own casing and power supply.
So, the clear distinction is that internal modems are expansion cards, while external modems plug into external ports like the serial port.
Option B correctly captures this difference.
Answer:B. Internal modems are PCI or ISA expansion cards, while external modems are traditionally plugged into a serial port on the computer.