Simplify the following text for a Grade 10 native English-speaking person.
Original: They were the first member of the Electrostar family , which also includes Classes 375 , 376 , 377 and 378 , and is the most numerous type of EMU built in the post-privatisation period of Britain 's railways .
Simplified: The Electrostar family also includes Classes 375 , 376 , 377 and 378 , and is the most numerous type of EMU built in the post-privatisation period of Britain 's railways .