The first assignment, I gave it to them, they came back in two weeks and they just blew me away. I mean the work was so beyond, literally, my imagination, because I had copied the process from Imagineering's VR lab, but I had no idea what they could or couldn't do with it as undergraduates, and their tools were weaker, and they came back on the first assignment, and they did something that was so spectacular that I literally didn't, ten years as a professor and I had no idea what to do next. So I called up my mentor, and I called up Andy Van Dam. And I said, Andy, I just gave a two-week assignment, and they came back and did stuff that if I had given them a whole semester I would have given them all As. Sensei, what do I do? [laughter] And Andy thought for a minute and he said, you go back into class tomorrow and you look them in the eye and you say, "Guys, that was pretty good, but I know you can do better." [laughter] And that was exactly the right advice. —“The Last Lecture,” Randy Pausch. What is the purpose of Pausch telling this story?

A.) He wants to show what a good teacher he was.
B.) He wants the audience to hire his former students as computer programmers.
C.) He wants to show that in order to encourage people, one should not limit what they can do.
D.) He wants to encourage other professors to give difficult assignments.