You use the . . . . . . . . tool to add a radio button to a form.

The correct answer is: D. RadioButton

A radio button is a type of button that allows the user to select one option from a group of mutually exclusive options. It is typically represented by a circle that is filled in when the option is selected.

The other options are incorrect because:

• A button is a generic term for a control that can be used to perform an action.
• Radio is a type of button that is used to select one option from a group of mutually exclusive options. However, it is not the correct answer because the question asks about the tool that is used to add a radio button to a form.
• Option is a generic term for a choice that can be made from a list of alternatives.

I hope this helps! Let me know if you have any other questions.