Simplify the following text for a Grade 7 native English-speaking person.
Original: The 1st century BC , also known as the last century BC or 1st century BCE , started on the first day of 100 BC and ended on the last day of 1 BC .
Simplified: The 1st century BC started on January 1 , 100 BC and ended on December 31 , 1 BC . An alternative name for this century is the last century BC .