题目选项分析

Charcoal being replaced by coal as the fuel used in the smelting of iron ore, and several improvements in blowing machinery, which tripled the average output of ironwork over the course of the eighteenth century.

Over the course of the eighteenth century, the average output of ironwork tripled as a result of several improvements in blowing machinery and because coal replaced charcoal as the fuel used in the smelting of iron ore.