Iron Production Was Transformed by Abraham Darby's Discovery That It

Iron production was transformed by Abraham Darby's discovery that it was much cheaper if

A) machines could do the work of hammering iron better than humans.
B) mills operated with hydroelectric power produced stronger iron.
C) coke was used in the place of charcoal in the smelting process.
D) taconite was a more valuable byproduct than the iron itself.
E) people worked better for higher wages.