You create a Web service.
The method in the Web service maintains session information between calls.
When a client invokes the method, the following exception is thrown :

System.Web.Services.Protocols.SoapException: Server was unable toprocess request. —> System.NullReferenceException: Object reference not set to an instance of an object.

You need to ensure that the Web service method can be called without generating an exception.

What should you do?

A.
Use the WebService.Session object instead of the HttpContext.Session object to access the session variables.

B.
Set the EnableSession property of the WebMethod attribute to True.

C.
Set the ConformsTo property in the WebServiceBindingAttribute attribute to WsiProvfiles.BasicProfile1_1.

D.
Set the AllowAutoRedirect property on the proxy class on the Web service client to True.