Right-clicking can also be used to insert sound files. This generates tags of the form <audio src="a.wav">. To play the sound again, press CTRL+R in the main window. You can also play a part of the audio file, as audio tags support start and stop arguments, e.g. start="1" stop="2"> will play the sound file from 1 to 2 seconds.
https://mnemosyne-proj.org/help/adding-media.php
Thanks!