Unless otherwise prescribed, what is the rule regarding level to be maintained by an aircraft flying IFR outside controlled airspace?
2 000 feet above the highest obstacle within 8 nautical miles of course
1 000 feet above the highest obstacle within 8 kilometres of the estimated position of the aircraft
2 000 feet above the highest obstacle within 8 kilometres of course
1 000 feet above the highest obstacle within 8 nautical miles of course