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.

A.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.
Correct.

B.Over the course of the eighteenth century a tripling in the average output of ironwork was due to the replacement of charcoal by coal for the fuel used in the smelting of iron ore, in addition to several improvements in blowing machinery.
Try to avoid passive constructions as much as possible. If you have an answer choice that is grammatically correct and uses active construction, use that

C.With charcoal’s being replaced by coal as the fuel used in the smelting of iron ore and several improvements in blowing machinery, the average output of ironwork tripled over the eighteenth century.
Usage of being is incorrect. The replacement has already been done in the 18th century.

D.The replacement of charcoal with coal for the fuel used in the smelting of iron ore and several improvements in blowing machinery, the average output of ironwork tripled over the eighteenth century.
A comma cannot be used to connect these two sentences

E.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
There is no working verb in this sentence