You are developing a client application that consumes a Windows Communication Foundation (WCF) service. You use the svcutil.exe utility to create a proxy for the service. You use the svcutil.exe switches that generate asynchronous calls. GetFlight is a service operation that takes no parameters and returns a string. The GetFlightCallback method must be called when the service operation returns.You create an instance of the client proxy with the following code:var client = new TranvelServiceClient（　）;You need to ensure that a callback is received when the GetFlight operation is called asynchronously. Which code segment should you use?（）

• A、client.BeginGetFlight(GetFlightCallback, null); client.GetFlight();
• B、client.GetFlight(); client.BeginGetFlight(GetFlightCallback, null);
• C、client.GetFlightCompleted += new EventHandler(GetFlightCallback); client.GetFlightAsync();
• D、IAsyncResult asyncResult = client.BeginGetFlight(GetFlightCallback, client); client.EndGetFlight(asyncResult);