单项选择题 You are creating a Windows Forms application by using the .NET Framework 3.5.You write the following code segment to bind a list of categories to a dropdown list.（Line numbers are included for reference only.） You need to ensure that the dropdown list meets the following requirements：  （1）Displays all category names   （2）Uses the category ID as the selected item value    Which code segment should you add at line 06？（）

单项选择题 You are creating a Windows Forms application by using the .NET Framework 3.5. You plan to modify a list of orders within a DataGridView control in the application. You need to ensure that a value is required in the first column of the grid control.  Which code segment should you use？（）

单项选择题 You are creating a multiple document interface （ MDI） application by using the .NET Framework 3.5 . You configure the frmParent form to be an MDI parent.You write the following code segment （Line numbers are included for reference only.） You need to associate and display the frmChild form and the frmParent form.   Which code segment should you add？（）