There needs to be a noun (or noun phrase) after 'due to'. You cannot have a clause after 'due to'. In that case, you should use "because of'.

Here, you have a noun phrase after 'due to', not a clause.
'the replacement' is a noun and 'the replacement of charcoal ...' is the noun phrase.
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Indeed, not a very commonly used construct that one would expect on GMAT.
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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.

HEY GUYS, A SIMPLE WAY TO ELIMINATE B
coal replaced charcoal as the fuel
the replacement of charcoal by coal for the fuel, "FOR" IS WRONG HERE

replace X with/by Y as sth
substitute X for Y

DON'T MIX THE IDIOMS, I THINK I DESERVE KUDOS!!
Please correct if I'm wrong.

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.

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.

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.

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.

GMATNinja Sir! Your explanation is desperately needed here. Why did we prefer a (A) over (B)?
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This one is all about meaning.

First, take another look at (A):


The sentence begins with the modifier in red. This phrase appears to be giving us the time frame for the action "tripled." This makes perfect sense. During this century, output tripled. So the output may have gone up a bit in 1714 and gone up some more in 1716, and over the course of this 100-year period, the increase accumulated so much that output tripled. Totally logical.

Contrast this with (B):


As Karishma noted in an earlier post, this modification makes no sense. "Over the course of the century," the tripling was due to the replacement of coal? What does that mean? That in 1714, the tripling was due to the replacement of coal and in 1716, the tripling was also due to the replacement of coal, and so on? Did the output triple every year over the course of the century and each time it tripled, it had the same cause? This is illogical.

The problem is that "over the course of 100 years" suggests a gradual process, but "was due to" isn't a gradual action that unfolds over time, the way "tripled" is.

Because (A) is logical and (B) is not, (A) is better.

I hope that clears things up!
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GMATNinja Thankyou for the explanation. But in (A) we compare a noun improvements with a clause coal replaced charcoal. How are they parallel. I understand that the logic and meaning trump everything else, but how to look beyond parallelism within 1.8 minutes during GMAT?
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