This type of question is generally asked by lazy interviewers who want to hear you talk for a while. A better question would be to separate the three positions and ask them one by one. But some people will ask this question, so you should definitely prepare for it. You can use this as your advantage. If you don't have many good things to say about your second position, you can briefly comment on it and spend more time talking about the other two positions. I'll give an example in the long answer, but here are some short answers first.
I haven't worked at three different positions, so I just made one up. The question is pretty general, so the answer is pretty general. It does emphasize sales skill and coming back to the type of work that this person enjoys. But you should think of something that is related to the position you are interviewing for. Only thing you should be concerned about it clearly explaining your past three positions, what you learned there, and if you did something notable, include that as well.
Learn English speaking much FASTER by downloading the TalkEnglish Offline Package and submerge yourself with over 8,000 audio files and over 800 pages of lessons! Then you can study without Internet connection and also listen to audio files using your MP3 player at any time. Go to the English Download page and download today!