Concept:Cobalt-60 is a common gamma-emitting radioisotope used in industrial radiography to inspect welds and castings for internal faults.Explanation:Industrial radiography uses gamma rays to penetrate metal and reveal hidden cracks or flaws.Cobalt-60 emits strong gamma rays and is widely used for this purpose.Therefore, the correct radioisotope is cobalt-60.Answer:C. cobalt-60