What type of depreciation is the most challenging to correct?

Wait — the question states the correct answer is C (Physical), but the explanation provided says 'External (economic) obsolescence is hardest to correct as it's caused by factors outside the property.' This is a factual inconsistency in the source question: the universally accepted appraisal principle, consistent with the Appraisal Institute's guidance and California real estate exam content, is that external (economic) obsolescence is the most difficult to correct because its causes lie entirely outside the property owner's control. Physical deterioration (answer C) is generally considered curable through maintenance and renovation, while external obsolescence (answer B) is almost always incurable. The correct answer based on established appraisal doctrine should be B, and the explanation aligns with B.