I'm not seeing anything in the iPad user guide about two different option buttons. I only see reference to the Calendars button, which I have on my iPad, and the Invitations button which, if that's the other one you are referring to, only appears if you're using an Exchange account and, I believe, have a meeting invitation pending. Do you not have that Calendars button showing on yours? If you don't, do you have multiple calendars set up in iCal on your computer, if you're using a Mac, or in whatever calendar application/service you are connected to? I'm not certain, but that button may not appear if you have only one calendar synched to your iPad.
Regards.
