C is to D. Enhancement is to reversal as retrieval is 
to obsolescence. I don’t know why, but it is. And it 
pans out, it works out. So this has an advantage if 
you found two and three of the four and you’re 
looking for the fourth, you know what kind of 
thing to look for. You know how to look, and you 
know how to recognize the answer when it comes. 
So you know how to recognize if things are a little 
bit off as well. It gives you a couple of cross 
checks. All of this was being done in the interest of 
bringing Understanding Media  up to date, about 14 
years after its publication. So we wrote it up and 
sent it to McGraw-Hill. We said, “Here’s the book. 
We’ve made a few corrections in accordance with