The Add Log Fields activity enables you to add custom information to logs related to transactions for tracing purposes1. The activity takes a collection of string arguments as input, which are added to every subsequent log message throughout the entire workflow, unless a Remove Log Fields activity is used1. The custom log fields can be useful for adding more information and visibility to the logs, especially for transactional data processes2. For example, you can use the Add Log Fields activity to add the transaction ID, the transaction status, the business process name, or any other relevant data to the logs2. Therefore, the correct answer is A. Add Log Fields.