单项选择题 You are developing a Windows Communication Foundation (WCF) service that does not operate on a duplex channel.You find that operations do not start until all previous operations have finished. The service hosting code contains the following lines.var service = new WarehouseService(); var host = new ServiceHost(service);You need to ensure that new operations do not wait for previous operations to finish. Which attribute should you use to decorate the service?（）

单项选择题 You are developing a Windows Communication Foundation (WCF) service that allows customers to update financial data. The client applications call the service in a transaction. 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 ... 10 class UpdateService : IDataUpdate 11 { 12 [OperationBehavior(TransactionScopeRequired = true, TransactionAutoComplete = true)]13 public void Update(string accountNumber, double amount) 14 { 15 try 16 { 17 ... 18 } 19 catch(Exception ex) 20 { 21 WriteErrorLog(ex); 22 ... 23 } 24 } 25 } 26Customers report that the transaction completes successfully even if the Update method throws an exception.You need to ensure that the transaction is aborted if the Update method is not successful. What should you do? （）

单项选择题 You are developing a Windows Communication Foundation (WCF) service that must be discoverable.You need to ensure that the ServiceHost instance supports multiple discovery versions. What should you do?（）