You are designing a Windows Azure application.  The application includes two web roles and three instances of a worker role.  The web roles will send requests to the worker role through one or more Windows Azure Queues. You have the following requirements：   - Ensure that each request is processed exactly one time.   - Minimize the idle time of each worker role instance. - Maximize the reliability of request processing.   You need to recommend a queue design for sending requests to the worker role.  What should you recommend？（）

• A、 Create a single queue.  Send requests on the single queue.
• B、 Create a queue for each web role.  Send requests on all queues at the same time.
• C、 Create a queue for each workerrole instance.  Send requests on each worker queue in a round robin.
• D、 Create a queue for each combination of web roles and worker role instances.  Send requests to all worker role instances based on the sending web role.