单项选择题 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?（）

单项选择题 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?（）

单项选择题 You create a Windows Communication Foundation (WCF) service. It is deployed on Microsoft Internet Information Services (IIS) with an application pool running as Network Service. You enable WMI tracing before launching the service. Your IT support staff adds WMI data collection through ASP.NET WMI tracing.You need to restrict the collection of WMI data to a privileged account. What should you do in WMI Control in the Computer Management console?（）