问题：

[单选]

You work as a Web Developer at Certkiller.com. You create a Web application using MicrosoftASP.NET 3.5. 
Certkiller.com hosts the application in Microsoft Internet Information Services 7.0. You attempt tobrowse the application and receive the following error message： 
Service Unavailable   
HTTP Error 503. The service is unavailable.  
You check and discover that you are able to browse successfully to other application that formspart of the same IIS Web site. The hosted applications on the network make use of ASP.NET 3.5.There are not previous versions of ASP.NET is installed. You need to resolve this error as soon aspossible. 
What should you do？（）

A . You should run the ServiceModel Metadata Utility tool (Svcutil.exe).
B . You should change the pipeline mode associated with the application pool that hosts theapplication.
C . You should run the ASP.NET Registration Tool (Aspnet_regiis.exe).
D . You should make sure that the application pool that hosts the application is initiated.