Sentence Correction

Rivaling the pyramids of Egypt or even the ancient cities of the Maya as an achievement, the army of terra-cotta warriors created to protect Qin Shi Huang, China's first emperor, in his afterlife is more than 2,000 years old and took 700,000 artistans more than 36 years to complete them.

(A) took 700,000 artistans more than 36 years to complete them
(B) took 700,000 artistans more than 36 years to complete it
(C) took 700,000 artistans more than 36 years to complete
(D) 700,000 artistans took more than 36 years to complete
(E) to complete them took 700,000 artisans more than 36 years

OA: C

Rivaling the pyramids of Egypt or even the ancient cities of the Maya as an achievement(modifier), the army(singular subject) of terra-cotta warriors created(verb) to protect Qin Shi Huang, China's first emperor, in his afterlife is more than 2,000 years old and took(second verb) 700,000 artistans more than 36 years to complete them.
D and E are out. We need a second verb followed by "and" (-->this is "hot" key to tell what to come next)
"them"(A) and "it"(B) are not necessary. Nix out.
Therefore, C is the correct answer.
(A) took 700,000 artistans more than 36 years to complete them
(B) took 700,000 artistans more than 36 years to complete it
(C) took 700,000 artistans more than 36 years to complete
(D) 700,000 artistans took more than 36 years to complete
(E) to complete them took 700,000 artisans more than 36 years

hitmewithgmat wrote:Rivaling the pyramids of Egypt or even the ancient cities of the Maya as an achievement(modifier), the army(singular subject) of terra-cotta warriors created(verb) to protect Qin Shi Huang, China's first emperor, in his afterlife is more than 2,000 years old and took(second verb) 700,000 artistans more than 36 years to complete them.
D and E are out. We need a second verb followed by "and" (-->this is "hot" key to tell what to come next)
"them"(A) and "it"(B) are not necessary. Nix out.
Therefore, C is the correct answer.
(A) took 700,000 artistans more than 36 years to complete them
(B) took 700,000 artistans more than 36 years to complete it
(C) took 700,000 artistans more than 36 years to complete
(D) 700,000 artistans took more than 36 years to complete
(E) to complete them took 700,000 artisans more than 36 years

How did you know "them" or "it" is not necessary? I knew "them" didn't agree with "army", but was unsure if "it" was needed or not.