You have an SQL query that takes one minute to execute. You use the following code segment to execute the SQL query asynchronously.IAsyncResult ar = cmd.BeginExecuteReader（　）;You need to execute a method named Do Work（　） that takes one second to run while the SQL query is executing. DoWork（　） must run as many times as possible while the SQL query is executing. Which code segment should you use? （）

• A、while（ar.AsyncWaitHandle==null）{DoWork（）；}dr=cmd.EndExecuteReader（ar）；
• B、while（!ar.IsCompleted）{DoWork（）；}dr=cmd.EndExecuteReader（ar）；
• C、while（Thread.CurrentThread.ThreadState==ThreadState.Running）{DoWork（）；}dr=cmd.EndExecuteReader（ar）；
• D、while（!ar.AsyncWaitHandle.WaitOne（））{DoWork（）；}dr=cmd.EndExecuteReader（ar）；