"To write off bad debt" means to remove or cancel an amount that was expected to be paid but is now considered unlikely to be collected. When a business determines that a debt is uncollectible, it needs to remove the amount from its accounts so that it can have a more accurate view of its financial situation. This process involves debiting the bad debt account and crediting the debtor's account. So, the answer is "bad debt account and credit debtor's account". The other options are incorrect as they do not accurately describe the accounting process for writing off bad debt.