[单项选择]You are developing a Windows Communication Foundation (WCF) service. The service needs to access out-of-process resources.You need to ensure that the service accesses these resources on behalf of the originating caller. What should you do?（）
A. Set the value of ServiceSecurityContext.Current.WindowsIdentity.ImpersonationLevel to TokenlmpersonationLevel.Impersonation
B. Set the value of ServiceSecurityContext.Current.Windowsldentity.ImpersonationLevel to TokenlmpersonationLevel.Delegation
C. Set the PrincipalPermissionAttribute on the service contract and update the binding attribute in the endpoint element of the configuration file to wsHttpBinding
D. Set the PnncipalPermissionAttribute on the service contract and update the bindingConfiguration attribute in the endpoint element of the configuration file to wsHttpBinding

[单项选择] You are developing a Windows Communication Foundation (WCF) service.One of the service operations contains the following code.private static int counter = 0;[OperationContract]public void IncrementCount（　）{ counter++;}You need to set a service behavior that prevents two or more threads from incrementing the counter variable at the same time. Which code segment should you use to set the service behavior?（）
A. [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single, ConcurrencyMode = ConcurrencyMode.Single)]
B. [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession, ConcurrencyMode = ConcurrencyMode.Single)]
C. [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single, ConcurrencyMode = ConcurrencyMode.Multiple)]
D. [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall, ConcurrencyMode = ConcurrencyMode.Reentrant)]