Well, I did my homework, of course, but then my dog ate it, and so I had to program my nanomachines to read the data from the remains of my homework inside my dog's stomach and transmit it to my computer so I could print out another copy.

Oh, wait, I don't have a dog. Never mind. Anyway, these aliens came and abducted my homework. Yes, that's what happened. They said they'd give me back my homework if I gave them some cheese. But I didn't have any cheese, and so I said, "Well, I had some cheese, of course, but then my dog ate it, and so I had to use nanomachines to assemble the carbon, hydrogen, oxygen, and nitrogen atoms and some minerals as well into molecules of the components of cheese. I did this on my computer, and then my dog ate it. Oh, wait, I don't have a dog. Never mind. Anyway, I don't have your cheese." That's what I told them, and then they got mad and destroyed everything. Among the things they destroyed was my homework.

And that's the reason why I don't have my homework. 'Cause my dog ate it.