Which code segment should you use?

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 TravelServiceClient(); You need to ensure
that a callback is received when the GetFlight operation is called asynchronously. Which
code segment should you use?

A.
IAsyncResult asyncResult = client.BeginGetFlight( GetFlightCallback, client);
client.EndGetFlight(asyncResult);

B.
client.BeginGetFlight(GetFlightCallback, null); client.GetFlight();

C.
client.GetFlight(); client.BeginGetFlight(GetFlightCallback, null);

D.
client.GetFlightCompleted += new EventHandler<GetFlightCompletedEventArgs>(
GetFlightCallback); client.GetFlightAsync();