licensing question, please help

Hi, I’m creating elearning presentations and I’ll be using some of the audio on the website. I read the faq but it confused me even more with “single end product” term. I’ll create a website and upload my presentations free to use for students but I’ll sell them to teachers who want to use them offline. Now my question:

Can I use an audio file I bought (let’s say clapping or some background music) on every presentation? or Will I need to buy the same audio files every time I make a new presentation? That’d be costly and deter me buying for even one presentation.