单项选择题 You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. You add a TreeView control to show the hierarchical structure of orders and order details. Each order contains an ObservableCollection named OrderDetails. You write the following code fragment. (Line numbers are included for reference only.) You need to ensure that the TreeView control meets the following requirements: Each order is shown as a TreeView node. The order nodes have order detail nodes as children. The order detail nodes have no children. Which code fragment should you insert at line 07?（）

单项选择题 You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. You add a ListBox to show grouped data. The ListBox is data-bound to a collection of items. Each item has the Name and State properties. You need to ensure that the ListBox meets the following requirements: Names grouped by State Names sorted in ascending order States sorted in descending order Which code fragment should you use?（）

单项选择题 You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. You add a ListBox control to the application. The ListBox control is data-bound to an instance of a custom collection class of the Product objects named ProductList. You need to ensure that changes to ProductList are automatically reflected in the ListBox control. What should you do? （）