Simplify the following text for a Grade 10 native English-speaking person.
Original: The longer-range 777-300ER and 777-200LR variants entered service in 2004 and 2006 , respectively , while a freighter version , the 777F , debuted in 2009 .
Simplified: The longer-range 777-300ER and 777-200LR variants entered service in 2004 and 2006 , respectively , while a freighter version , the 777F , first flew in 2008 .