Final answer:
When connecting a microphone, the microphone's XLR cord should be inserted into the interface's Mic input to ensure proper signal transmission and reduce noise.
Step-by-step explanation:
When connecting a microphone to an interface, the microphone's XLR cord should be inserted into the interface's C) Mic input. This is because the microphone input is specifically designed for the low-level signals that microphones produce. The XLR connectors provide a balanced connection which helps in reducing noise and interference. It is essential to use the mic input for microphones instead of the other inputs because they have different sensitivities and impedance levels that are suitable for different types of audio sources.