It can be inferred from the passage that the use of flux in processing copper ore can alter the lead isotope composition of the resulting metal EXCEPT when A. there is a smaller concentration of lead in the flux than in the copper ore B. the concentration of lead in the flux is equivalent to that of the lead in the ore C. some of the lead in the flux evaporates during processing D. any lead in the flux has the same isotopic composition as the lead in the ore E. other metals are added during processing