Hi Susan,

You can clear radiot buttons by creating a button with a rule that sets the
radio buttons' field to "". You can do this with a rule anywhere, in fact,
but a button probably makes the most sense.

Radio buttons are designed to make you choose one. If you want "none of the
above" to be an option, consider making another choice for that instead of
leaving it blank. That way you know the user didn't just forget to fill it in.