Explanation:Correct Option: A. The DeLee and Charnley system divides the AP radiographic appearance of the acetabulum into three zones. Zone 1 is the superior third (the weight-bearing dome), Zone 2 is the middle third, and Zone 3 is the inferior third near the teardrop. Progressive radiolucency in Zone 1 is highly concerning for mechanical loosening. (Ref: DeLee and Charnley, Clin Orthop Relat Res, 1976)