Simplify the following text for a Grade 7 native English-speaking person.
Original: Berlin 's underground ( Untergrundbahn , U-Bahn ) and Berlin 's S-Bahn ( a metropolitan public transit network ) , rebuilt after the war , continued to span all occupation sectors .
Simplified: In many ways Berlin worked as a single city . The U-Bahn and S-Bahn public transit networks , rebuilt after the war , spanned all occupation sectors .