Audio File with CC to only play once

I'm not sure what you want here, but if you want the audio to pause while another layer is showing, then resume when it is hidden, all you need to do is go to the layer properties, and select "pause timeline". Pausing the timeline stops everything including the audio.

If you want to prevent the learner from clicking on a layer until the audio finishes, then you need to change your variable when the media completes, and show the layers if the variable shows the audio has completed.