Simplify the following text for a Grade 10 native English-speaking person.
Original: British Rail Class 313 electric multiple units were built by BREL at York Works between February 1976 and April 1977 and were the first second-generation EMUs to be constructed for British Rail .
Simplified: Class 313 electric multiple units were built by BREL at York Works from 1976-77 , these being the first second-generation EMUs to be constructed for British Rail .