You are creating an application that consumes a Windows Communication Foundation (WCF) service. The service implements the IService contract. The client application contains the CallbackHandler class, which implements IServiceCallback.You need to ensure that a client proxy is created that can communicate with the service over a duplex channel.
Which code segment should you use?（）

You are creating a Windows Communication Foundation (WCF) service that uses claims-based authorization. The following code retrieves the correct claim set.var claims = ServiceSecurityContext.Current.AuthorizationContext.ClaimSets[0];You need to validate that the requesting client application has included a valid DNS value in the claim.
Which code segment should you use to retrieve the claim for validation?（）