Explanation:

Correct option 4: System Bus

1. Data Bus – Carries data between CPU, memory, and other devices

2. Address Bus – Carries memory addresses from CPU to other components

3. System Bus – Includes data, address, and control buses; it's the main bus architecture used to connect components (including external ones via interfaces)

4. Control Bus – Carries control signals (like read/write commands)

So, among the given options, the most appropriate and comprehensive one to connect external devices is: