Final answer:
The correct answer is option 3. The Terracotta Army is the historical site associated with Emperor Qin Shi Huangdi, featuring thousands of life-sized clay statues as part of his mausoleum near Xi'an, discovered in 1974 and now a UNESCO World Heritage site.
Step-by-step explanation:
The historical site known for containing thousands of life-sized military figures and associated with the Chinese emperor Qin Shi Huangdi is the Terracotta Army.
This remarkable archaeological discovery includes a vast collection of clay statues of soldiers, officials, servants, and horses buried with the emperor to protect him in his journey to the afterlife.
Constructed during the rule of Qin Shi Huangdi, the founder of the Qin dynasty, the Terracotta Army was a massive project that began shortly after he ascended the throne in 221 BCE and utilized the labor of commoners in lieu of taxes or as a legal requirement.
The site of the emperor's mausoleum is a UNESCO World Heritage site and was unearthed in 1974 near Xi'an, revealing the extent of Shihuangdi's quest for immortality and security after death.