Complex sentence: The mark and sweep strategy has the advantage that, once the unreachable set is determined, either a moving or non-moving collection strategy can be pursued; this choice of strategy can even be made at runtime, as available memory permits.
Split into simpler sentences: The mark and sweep strategy has the advantage that, once the condemned set is determined, either a moving or non-moving collection strategy can be pursued. This choice of strategy can be made at runtime, as available memory permits.