The main purpose of a control account in accounting is to detect errors and irregularities in the recording and posting of transactions in the individual accounts. A control account is a summary account that reflects the total of a group of related accounts. By comparing the total of the individual accounts to the balance of the control account, it is possible to quickly identify any discrepancies and investigate the causes of any discrepancies. This helps to ensure the accuracy and completeness of the accounting records and enhances the reliability of financial information used for decision-making purposes. Therefore, option A, "detect errors and irregularities," is the correct answer. The other options are not relevant to the purpose of a control account.