Use radio buttons when the client should choose one of several alternatives.
1. Place the field
In an editable proposal, open Content → Fields → Radio buttons and place it near the question.
2. Enter one group of choices
In the field settings, name the question and add its answers to the same group. Turn on required only if the client must make a choice.
3. Check selection
Save and preview. Choose two answers in turn. Selecting the second should clear the first.