Hi Chrissy,
If I understand your question correctly, the answer is "one".
Radio buttons are meant to limit the user response to a question to one
answer. This means that if the question has three possible responses, if you
check one radio button, then change your answer and click another one, the
first one you check will become unchecked.
If you want the user to be able to check more than one answer, you would
have to use check boxes. They allow more than one answer to be checked.
Hope that answers your question. Good luck.