Explanation
The correct answer is C, Request-Reply: Enhanced External Services invokes a REST API. This is because Enhanced External Services allows you to register an external web service that has an OpenAPI 2.0 specification and use it as an invocable action in a Lightning flow. This way, you can check the preferences from the external service in real-time and get the response in Boolean and string values. The other options are not suitable for this scenario because:
A, Fire and Forget: Process-driven platform events publishes events on Salesforce Event Bus, is a pattern that is used for asynchronous integration, where the sender does not expect a response from the receiver. This is not suitable for checking preferences in real-time.
B, Remote Call-In: Salesforce REST API with REST Composite Resources, is a pattern that is used for integrating external applications with Salesforce by calling the Salesforce REST API. This is not suitable for invoking an external service from a Lightning flow.
D, Data Virtualization: Salesforce Connect map data external REST data in external objects, is a pattern that is used for accessing external data without copying or synchronizing it to Salesforce. This is not suitable for checking preferences in real-time or using them in a Lightning flow.
References:
Enhanced External Services
Get Started with External Services
Registering external services in salesforce