Non-verbal communication refers to a way of conveying information in a face-to-face situation without the need of speaking.
The three options provided in the answer are appropiate in this case, given that eye contact relies on eye movement, facial expressions rely on moving one's face, and gestures consist of body movements; none of these involve speaking up.
Both the first one and the last one could be correct here, but choosing which one is best would probably be the last one becasue the biggest difference, or what sets the two apart is primarily who is around.
