Choice "C" is correct. Manufacturing overhead is not an element of the manufacturing processing you would expect to see in a cause and effect (fishbone) diagram. It is an allocated cost.
Choice "a" is incorrect. Manpower, machinery, methods, and materials are commonly identified elements of manufacturing processes that would be used to evaluate the source of defects. Manpower is an element of the manufacturing process typically presented on a cause and effect (Fishbone) diagram.
Choice "d" is incorrect. Manpower, machinery, methods, and materials are commonly identified elements of manufacturing processes that would be used to evaluate the source of defects. Machinery is an element of the manufacturing process typically presented on a cause and effect (Fishbone) diagram.
Choice "b" is incorrect. Manpower, machinery, methods, and materials are commonly identified elements of manufacturing processes that would be used to evaluate the source of defects. Method is an element of the manufacturing process typically presented on a cause and effect (Fishbone) diagram.