I had to do a powerpoint in astronomy with this senior (I'm a freshman), and I basically did ALL the work. I spend literal hours in the library educating myself on the topic, and for the powerpoint there are certain slides that I will be able to explain and he won't, simply because he did not put in the time. He doesn't know how many hours I put into this thing, and I need to be the one to explain certain slides. How can I tell him that I need to do those particular ones without flat out saying, "because you would have no idea of even the first thing on that slide". Some information that needs to be said is not directly written on the slide. If he did it, he would omit that information.
I need to let him know that he simply can't explain those slides without making myself sound like I'm putting him down.