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 artisans more than 36 years to complete them.A. took 700,000 artisans more than 36 years to complete them-> The army.....took 700,000 artisans more than 36 years to complete. "Them" is incorrect.
B. took 700,000 artisans more than 36 years to complete it->The army.....took 700,000 artisans more than 36 years to complete. "it" is incorrect. Because it refers to singular noun the Army, but we don't need it.
C. took 700,000 artisans more than 36 years to complete-> It is better. Let's keep it.
D. 700,000 artisans took more than 36 years to complete-> Now, subject is 700,000 artisans. Which should be The army.
E. to complete them took 700,000 artisans more than 36 years-> "them" need singular pronoun as subject is singular.
So, I think C.