Render method of the base page

 I have a page called derivedPage.aspx. This page inherit from a c# class baseClass.c. This baseClass.c inherit from web.ui i.e. it is providing common functionality. Now I am trying to find the content place holder (of master page with FindControl method) in the render method that has been declared in the baseClass.c. I try to loop through all the control and diplayed them on the screen, but i am unable to find the content place holder of  master page

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