One of our teachers just asked me how to add sound to a Google Drive presentation. I like this tutorial explaining the answer as it shows how you can actually go to a specific spot in a video. Therefore when you click on the spot on a slide it will play exactly what you want. For example, if you click on this link, you will go exactly to the part of the video above that tells how to get to a specific spot in the video.
While we are at it the teacher also wanted to know how to add in animation which is done in the video below.