David Letterman will keep his "Stupid Pet Tricks" on CBS.

What was David Letterman thinking when he turned down ABC and decided to stay with CBS?

A. He really didn't want to be responsible for Ted Koppel losing his job, even though Koppel is not a particularly funny guy.

B. CBS promised to call off the Mike Wallace/"60 Minutes" investigative piece on Letterman's real relationship to the woman who kept "breaking" into his house.

C. CBS promised to "try" to stop Howard Stern from saying all those terrible things about him.

D. He really wanted to give "Monday Night Football" a shot, but ABC said that was a deal-breaker.

E. CBS promised he would never have to have any of the following annoying people on his show -- Donald Trump, *N Sync or the Backstreet Boys, the French skating judge, the kid from the Dell commercials, Enrique Iglesias or any husband (past, present or future) of Rosanne Barr.

F. Although Letterman's executive producer Rob Burnett said the deal wasn't about money, the $71 million per year in salary and producing fees did not hurt.