You are developing a Windows Communication Foundation (WCF) service that allows customers to update financial data. The service contract is defined as follows. (Line numbers are included for reference only) 01 [ServiceContract] 02 public interface IDataUpdate 03 { 04 [OperationContract] 05 [TransactionFlow(TransactionFlowOption.Mandatory)] 06 void Update(string accountNumber, double amount); 07 } 08 09 class UpdateService : IDataUpdate 10 { 11 [OperationBehavior(TransactionScopeRequired = true, TransactionAutoComplete = false)] 12 public void Update(string accountNumber, double amount) 13 { 14 ... 15 } 16 } 17 You need to ensure that the service is invoked within the transaction. What should you do?（）

• A、Replace line 01 with the following code [ServiceContract(SessionMode = SessionMode.NotAllowed)]
• B、Replace line 01 with the following code [ServiceContract(SessionMode = SessionMode.Required)]
• C、Call the Invoke method of the form and supply a delegate.
• D、Call the BeginInvoke method of the form and supply a delegate.