Read the following passage about Diên Khánh Citadel and mark the letter A, B, C, or D on your answer sheet to indicate the best answer to each of the following questions from 23 to 30.

Diên Khánh Citadel is a historical fortress located in Khánh Hòa province, Vietnam. Built in 1793 during the Tay Son Dynasty, it served as a military stronghold and administrative center. The citadel was constructed in the Vauban style, which was characterized by star-shaped fortresses with multiple layers of defense. This design made the citadel highly resistant to attacks and allowed for efficient use of artillery.

The citadel's walls are made of stone and earth, standing approximately 3.5 meters high and spanning a circumference of about 2.5 kilometers. There are six main gates, each facing a different direction, symbolizing the openness and strategic importance of the fortress. Inside the citadel, various buildings and structures once housed military officials, soldiers, and administrative personnel.

Diên Khánh Citadel played a significant role in the military history of Vietnam. It was a site of numerous battles and witnessed the rise and fall of several dynasties. Today, the citadel is a popular tourist attraction, drawing visitors interested in exploring Vietnam's rich history and architectural heritage. The well-preserved walls and gates, along with the lush greenery surrounding the site, offer a glimpse into the past and a tranquil escape from the bustling modern world.

Efforts to preserve and restore Diên Khánh Citadel have been ongoing. Local authorities and historians work together to maintain the integrity of the site while promoting its historical and cultural significance. Educational programs and guided tours help raise awareness about the importance of preserving such historical landmarks for future generations.

Which dynasty built Diên Khánh Citadel?