Whenever you respond to a question in the viva, remember that you need to offer evidence. A question might be seeking information; you need to provide it. A question might ask if you are correct; you can’t simply say yes. You need to offer evidence – context, information, reasons – that help show that you are correct.
Whenever you receive a question in the viva, remember that it is being asked for a reason. The evidence of your thesis, the story, facts and figures you have written up, have given your examiners plenty to think about. The evidence of your thesis prompts the questions that you are being asked to drive the discussion.