Which HTML format to use - 20 available!!

I am trying to use an HTML WYSIWYG program named Coffee Cup. The first question it asks is which HTML format I wish to use. I have NO clue which to use. My pages are EXTREMELY simple. Nothing fancy at all. The default for this software is 5.0. However, it does not permit the wysiwyg feature to be used and asks the user to choose another. I have a screenshow of the choices included with this question. One bit of advice given to me was 4.0. However there are THREE versions of 4.0 and I don't know the difference. I sure need some help.