Final answer:
The app used to authenticate your Marketing Cloud account with a Salesforce org is the Marketing Cloud Connector. It enables the integration between Salesforce CRM and the Marketing Cloud for data synchronization and campaign management.
Step-by-step explanation:
To authenticate your Marketing Cloud account with your Salesforce org, you would typically use the Marketing Cloud Connector. The connector allows for the integration of Salesforce CRM and the Salesforce Marketing Cloud, enabling features such as synchronized data, tracking, and the ability to send email campaigns directly from the Salesforce platform. The other options, like Salesforce Authentication Manager, Distributed Marketing Authentication, and Cloud Integration Hub, are not standard solutions for this specific type of authentication and integration between Marketing Cloud and Salesforce.