SC Question

[plasma_2000_in]

The invention of the cotton gin, being one of the most significant developments of the nineteenth century, had turned cotton cloth into an affordable commodity; it was costly before that

Correct Answer Option (D) is below

one of the most significant developments of the nineteenth century, turned cotton cloth into an affordable commodity, whereas it had previously been costly

My question is, here use of "it" - is it not ambiguous? Does "it" refer to "The Invention" or "Cotton Cloth"? Can someone please explain?

[nbf1186]

"It" refers to cotton cloth. It is not ambiguous because the construction of affordable.... whereas....costly logically links "cotton cloth" and "it".

[jnelson0612]

What is the original source of this question?