A is correct ... all aspects are in parallel form.

Sent from my SM-J210F using GMAT Club Forum mobile app

the flawless proportions and balance, the remarkable precision that should have been impossible to achieve without modern tools, and its rapid construction in less than ten years

What about its?

aaba , would you please check Answer C and edit the prompt if the transcription is inaccurate?
It looks like a copy-and-paste error.

Priyansha7 , I suspect you are uncomfortable with "the . . ., the . . ., its . . ."
The sentence gives three examples of the Parthenon's architectural "genius": proportions and balance; precision; and rapid construction.
All three are nouns.
"Its construction" is okay here.

First, and by far the most important decision point, the other four answers are clearly wrong. Truly awful. All four butcher parallelism.
Answer B: it was rapidly constructed is not a noun
Answer C: in less than ten years does not maintain the structure of [article - adjective - noun(s)]. In addition, it was rapidly constructed is not a noun.
Answer D: "should have been" . . . remarkable precision" is not parallel and is not grammatically correct.
"should have been . . . precision" needs an "it" or a "that which" before "should have been. . . " Finally, and in less than ten years its construction makes the entire sentence incomplete.
Answer E: "should have been . . . THAT remarkable precision" has the same problems as D, plus the incorrect use of "that" instead of "the."
Answer E has the trap: the construction that took place in less than ten years. Do not fall for the trap. The phrase "construction that took place" is redundant. The phrase is similar to saying, "the occurrence that occurred." Really, you should not even get to the trap. Read the "should have been" clause, see that it is a mess, and cross off both D and E immediately.

Second, in Answer A, although its is a possessive pronoun instead of a definite article, its still introduces [adjective-noun] in keeping with the list of examples.
Answer A is the only sentence that maintains parallelism of exemplary nouns that describe architectural genius.

Third, in a sentence thick with description about architecture, its is probably better than the to introduce a very broad categorical noun, "construction." Take a look at the sentence with "the" instead of "its":

Archaeologists, architects, and civil engineers trying to repair the 2,500- year-old architectural wonder known as the Parthenon are still struggling to understand several aspects of its genius: the flawless proportions and balance, the remarkable precision that should have been impossible to achieve without modern tools, and THE rapid construction in less than ten years.

Problem? My next question is, "The construction OF WHAT? Is there something else inside the building that this author forgot to mention?"
This sentence discusses the architecture of a huge building. Many things -- pillars, walls, and gables -- underwent "construction."
Stated differently, the word "construction" as a categorical noun in this architectural-construction context could cause confusion without the modifier "its."
"Its" tells us which construction happened in less than ten years. (Which construction? The construction of the whole building.)
This third point is subtle. There is no rule for it. But there is logic to it. This section requires verbal reasoning.

Hope that helps.
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