Sound files playing over each other

Hello.

I've created a drag & drop slide (attached) which enables users to click on a sound icon which will then play a voice file which indicates which object should be dragged and dropped into the drop box beside each sound icon. That all works fine except for the fact that if a user clicks on a sound icon before another sound icon has finished playing then the two sound files play over each other.

I've tried to fix this by creating variables and setting conditions but then the original sound file doesn't play. To counter that I have copied the sound file so I can point the condition to it and that works but then the original voice file plays as soon as the slide is opened (i.e. plays without being activated by the user!).  (NB: I've deleted the variables and conditions from the sample slide attached).

Does anyone know if I can get around this problem please?

Thank you.