Do Audio Books have to be CD's or are cassette tapes ok too ?

I believe either is ok, don't know why it wouldn't be.  although cassettes are becoming somewhat extinct!

Both CD & Cassette audios are acceptable. When posting them, if it is not stated on the listing whether it is abridged or unabridged, please while you have the audio in hand, submit a data corrections adding this info to the title. It will be greatly appreciated.