Sentence Correction (SC) | Re: Rivaling the pyramids of Egypt or even the ancient cities of the Maya

empowergmatverbal mentions that Choice B is not parallel because of the "it". To make Choice B correctly parallel, keeping "took 700,000 artisans more than 36 years to complete it", how would you make the first element "is... old" parallel? I am just confused as to where you would be an "it" in the first element.

Can someone also explain to me why Choice D is not parallel?
empowergmatverbal says Choice D is incorrect
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