You are designing a Windows Azure application.  Messages will be placed into a Windows Azure Queue and then processed by a worker role.  There is no requirement for adherence to the Windows Azure Service Level Agreement （SLA）.   You need to recommend an approach for concurrently processing messages while minimizing compute cost.  What should you recommend？（）

• A、 A single role instance that processes messages individually
• B、 A single role instance with multithreaded request processing
• C、 Multiple role instances that process messages individually
• D、 Multiple role instances， each with multithreaded request processing