【单选题】
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.  <br /> What should you do？（）
A、Implement theActivated event
B、Implement the MdiChildActivate event
C、Override the OnParentVisibleChanged method
D、Override the OnParentBindingContextChanged method
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