Simplify the following text for a Grade 7 native English-speaking person.
Original: The northern parts were once covered by veen ( bogs ) which separated the dryer and more arable south from Drenthe and which have been exploited as fuel to a large degree .
Simplified: The northern parts were once covered by veen ( bogs ) which separated the dryer and more arable south from Drenthe . These bogs have been exploited as fuel to a large degree .