What should you do?

A Windows Communication Foundation (WCF) service has a callback contract. You are developing a client application that will call this service.
You must ensure that the client application can interact with the WCF service. What should you do?

A.
On the OperationContractAttribute, set the AsyncPattern property value to true.

B.
On the OperationContractAttribute, set the ReplyAction property value to the endpoint address of the client.

C.
On the client, create a proxy derived from DuplexClientBase<TChannel>.

D.
On the client, use GetCallbackChannel<T>.

Explanation:
DuplexClientBase<TChannel> Class Used to create a channel to a duplex service and associate that channel with a callback object.

DuplexClientBase<TChannel> Class
(http://msdn.microsoft.com/en-us/library/ms576169.aspx)