A casino is implementing Salesforce and is planning to build a customer 360 degree view...

Exploring external data sources in Salesforce to build a 360 degree view of the customer (option A) is the best strategy to satisfy this requirement, as it allows customer service agents to view the activities from all four systems in real time without storing or replicating the data in Salesforce. Using a customer data mart to create the 360 degree view of the customer (option B) is not a good strategy, as it may introduce additional complexity and cost, and it does not leverage the native Salesforce features. Periodically uploading summary information in Salesforce to build a 360 degree view (option C) is also not a good strategy, as it may cause data latency and inconsistency, and it does not provide real-time information. Migrating customer activities from all four systems into Salesforce (option D) is also not a good strategy, as it may cause data redundancy and conflicts, and it does not scale well with large volumes of data.