A variant on multiple choice answers...

One in which you can only choose one choice at a time through Javascript:

Screen Shot 2013-02-17 at 9.19.44 AM.png

What you can't really see here is that if you choose "None of the above" it will make "enterprise" grayed out and unselect it if you had selected it. So, yes, it uses checkboxes to allow for multiple answers, but semantically it really only allows one answer right now (I think somebody was lazy and forgot to fill the list of the major car rental companies there).