Winning by Jack Welch

The other day I was taking a drive up to New Hampshire and I had an opportunity to listen to some of Jack Welch's audio book Winning. There is a section in the book about hire good people and if you had to ask one interview question what would it be. Mr. Welch felt that a really good interview question is to ask potential candidates:

"Why did you leave your last job and the one before it?"

What are some of your favorite interview questions to building a great team?