You can use the selection tools to select an interior surface of a model; for example, when you create a surface or when you select a region using the solid offset mesh tool.
To select an interior surface:
Use a display group to remove items from the display to expose the desired surface. For more information, see “Creating or editing a display group,” Section 51.2.1.
Click on the selection options tool 
in the prompt area to display the Options toolbox.
In the Options toolbox, toggle on the Select From Interior Entities tool 
.
Select the interior surface from the viewport.
