TOEFL Listening: TPO-TOEFL阅读TPO - S44S9VOGT5485H4IN$

Which of the following is NOT mentioned in paragraph 5 as a development that greatly changed the production of iron? A. The use of coke in the smelting of pig iron B. The invention of a furnace that used coke to refine iron C. The discovery of a method for increasing the production of charcoal D. The invention of powerful machinery that could shape, form, and finish iron