How do I create option groups in Excel?

Can anybody give me instructions on how to create an option group in MS Excel? I want to have a series of questions with Yes / No option buttons next to them. This works fine for the first question (2 opt buttons) but when I add the next 2 buttons for the 2nd question they are connected to the first pair of buttons. I.E., the four buttons act as a group of 4 instead of two, independent groups of 2 ! Thanks!