The key question for choosing an NDT method is how deep into the part it can actually see. Visual inspection only catches what is on the outer surface, penetrant testing only reveals cracks that are open right at the surface, and magnetic particle testing barely reaches a couple of millimetres below the surface in magnetic materials. Radiography works completely differently, since X-rays or gamma rays pass straight through the full thickness of the part and get absorbed differently wherever there is a void, crack, or inclusion inside, leaving a shadow image on film or a detector. Because it can reveal flaws buried deep inside the material, radiography is the method suited to internal defects, option (A).