单项选择题 You use Microsoft .NET Framework 4 to create a Windows Forms application. The application includes a RichTextBox control and a ListBox control. The ListBox control is populated with a list of valid file names. The application allows users to drag a ListBox item to the RichTextBox control. You need to provide a visual indication that a file that is dragged can be dropped on the RichTextBox control. What should you do?（）

单项选择题 You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. The application uses the drag-and-drop functionality. You need to ensure that the drag-and-drop operation is stopped when a user moves the cursor outside the boundaries of the application form. Which enumeration member should you use?（）

多项选择题 You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. The application uses the background worker process (BWP). When the user clicks a button, the background worker executes a method named DoCalculations asynchronously. You need to implement a progress bar on the user interface (UI) that informs the user of the progress of DoCalculations. Which two actions should you perform?（）