Which of These Factors Led to the Development of Low-Cost,high-Quality

Which of these factors led to the development of low-cost,high-quality iron?

A) The desire to produce smaller, purer batches with less expense
B) The high price of wood
C) The ability to remove impurities from coal and produce a concentrated coke product
D) The need to stretch available coal supplies
E) The high cost of energy used in smelting iron