You are creating a Windows Forms application for a financial service provider by using the .NET Framework 3.5. You have to implement a multiple document interface （MDI） in the application to allow users to open multiple financial documents simultaneously.You need to ensure that whenever the child MDI form is created， the application displays a message in the title bar of the parent MDI that a child form has received focus. What should you do？（）
- AImplement theActivated event
- BImplement the MdiChildActivate event
- COverride the OnParentVisibleChanged method
- DOverride the OnParentBindingContextChanged method