Simplify the following text for a Grade 9 native English-speaking person.
Original: Class 316 and Class 457 were TOPS classifications assigned to a single electric multiple unit ( EMU ) at different stages of its use as a prototype for the Networker series .
Simplified: Class 316 and Class 457 were two suggested TOPS classifications . They were given to a single electric multiple unit ( EMU ) at different stages of its use as a prototype for the Networker series .