Shit, what did I do!!! One of my students emailed me, saying that he got grade on the paper which he didn't write or hand in. When I read his email, my face became pale. I quickly logged in the gradebook and found that I had made a big mistake. Simply put, I messed up. I called the instructor to ask what to do. The thing which made it worse is that I didn't have a backup. He told me to email all of my students to return their papers. Of course, he was mad, or disappointed. Anyhow, I emailed all my students to return their paper. I hope they are honest and patient.