D. It was China's first great unified empire.
The Qin dynasty (221-206 BCE) was the first dynasty to unify China under a single ruler. It was founded by Qin Shi Huangdi, who conquered the six other major states and established a centralized imperial government. The Qin dynasty also standardized weights, measures, and the written language, and built the Great Wall of China to protect against invasions. However, the Qin dynasty was also known for its harsh legalism, which imposed severe punishments on those who violated the law.