You are developing an application that performs file backups in the background. The background application will host a Windows Communication Foundation (WCF) service and must be active as soon as the machine is running. The background application will not have a user interface. A front-end application will consume the WCF service and will provide the user interface.You need to choose a host environment for the WCF service. Which hosting environment should you choose? （）

• A、Microsoft Internet Information Services (IIS) 6.0
• B、Windows Process Activation Services (WAS)
• C、A Windows Forms application
• D、A Windows Service