Complex sentence: The Mountains of Mourne are partly owned by the National Trust and see a large number of visitors every year; their highest mountain is Slieve Donard at 849 metres (2,786 ft).
Split into simpler sentences: The Mountains of Mourne are partly owned by the National Trust and see a large number of visitors every year. The highest mountain is Slieve Donard at 849 metres (2,786 ft).