单项选择题
A. Implement the INotifyPropertyChanged interface in the Product class.
B. Implement the IQueryable<Product> interface in the ProductList class.
C. Extend the DependencyObject class in the Product class.
D. Extend the ObservableCollection<Product> class in the ProductList class.
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. The number of items of the data-bound collection is fixed. However, users can modify the properties of each of the Product objects in the collection. You need to ensure that changes made on the Product objects are automatically reflected in the ListBox control. What should you do?（）
单项选择题 You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. You write the following code fragment. You need to implement the MyProject.AverageConverter class. What should you do?（）
单项选择题 You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. You write the following code fragment. You need to implement the MyProject.MyConverter class. What should you do?（）