Which of the following is one of the connections required between a computer and a transceiver to operate digital modes?
Why Digital modes are just audio tones passed between the radio and the computer's sound card. Received signals come out of the transceiver's speaker or headphone jack and must go into the computer's "line in" (or mic in) so the software can decode them. In the other direction, the computer's "line out" feeds the transceiver's microphone or accessory audio input, and keying is handled separately by a serial/USB control line or VOX.
Watch out The choices involving push-to-talk are wrong because PTT is a keying control line, not an audio signal, so it never connects to a sound card jack. Computer "line out" to the speaker connector would push audio into a speaker output, backwards for both devices.
Audio flows out of the radio's speaker into the computer's line IN; computer line OUT goes to the mic input.