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？（）

• A、A
• B、B
• C、C
• D、D