Mark works as a Software Developer for McRobert Inc. He develops an ASP.NET application, named App1, using Visual Studio .NET. App1 retrieves purchase orders data from a SQL Server database and displays it in a DataGrid control, named DataGrid1. Mark wants to enable users to sort data in ascending or descending order, whenever they click a column. He writes code to sort the data in DataGrid1 using the SortOrder property. The SortOrder property stores a value "ASC" for ascending order and "DESC" for descending order. Mark wants to preserve the value during postbacks. Which of the following properties of the Control class will Mark use to accomplish this?