Hint: Don't say, "Make a baby"
Test Tube, a very cool short video featuring Canadian scientist and environmental activist David Suzuki has a trick question at the very start. Just take my advice on it, OK?
My only quibble is that the film gives the strong impression that population growth is exponential--the old Mathusian fallacy. (The gunman who recently took over the Discovery Channel headquarters before being shot and killed turns out to have been an adherent.) In fact, growing access to family planning services and changing economic signals (you don't need ten kids to help you work the farm anymore) are bringing down birthrates the world over. In the United States the fertility rate has dropped to 13.5 per 1,000 inhabitants, the lowest rate ever. On the other hand, population growth is expected to continue through at least mid-century while resources remain finite. That's why the old bumper sticker was so funny: one planet is all we get.