What is the correct DataWeave expression to retrieve the value CA from an API request URL?

The correct choice utilizes the DataWeave expression that directly accesses the URI parameters from the API request context. In MuleSoft, attributes such as uriParams are specifically designed to retrieve values from the URL parameters of an incoming HTTP request.

By using #[attributes.uriParams.state], the expression efficiently pulls the value associated with the key "state" from the URL parameters of the incoming API request. This is the most direct and appropriate way to access URL parameter data in a Mule application.

The other options, while referencing different parts of the message or properties, do not specifically target the URI parameters in a manner that retrieves the state value as cleanly and straightforwardly as option C does. For instance, message payload or inbound properties might not necessarily point directly to the URI parameters unless structured in a specific way, which makes C the most reliable and efficient choice for this scenario.