The correct answer is C: Computer 'line in' to transceiver speaker connector. When connecting a computer to a transceiver for digital mode operation, the computer's 'line in' (audio input) connects to the transceiver's speaker connector (audio output). This allows the computer to receive and decode the audio signals from the transceiver. The transceiver's speaker output contains the received audio signals that the computer needs to decode. By connecting the computer's line-in to the transceiver's speaker output, the computer can 'hear' what the radio is receiving and process it for digital mode decoding. This is one direction of the audio connection - you also need the reverse (computer audio out to transceiver mic in) for transmission.