messaging-based communication model

Which of the following statements are true? Select one or more a. In a messaging-based communication model, the client sends an xml document and the server application receives the xml as a W3C document object for processing. It is MANDATORY for the service to send a response back to the client. b. In a RPC-based communication model, a service client invokes the exposed method and a response is returned c. In a RPC-based communication model, a service client invokes the exposed method and a response is NOT returned d. In a messaging-based communication model, the client sends an xml document and the server application receives the xml as a W3C document object for processing. It is NOT MANDATORY for the service to send a response back to the client.