Simplify the following text for a Grade 9 native English-speaking person.
Original: The core of the Regional Rail system is the Center City Commuter Connection composed of three Center City stations in the `` tunnel '' corridor : the above-ground upper level of 30th Street Station ; and the underground Suburban Station ; and Market East Station .
Simplified: The Center City Commuter Connection connects the thirteen lines . The core stations in the CCCC are Suburban Station , the elevated 30th Street Station and Market East Station .