The correct answer is: A. Agra Fort
The Agra Fort is a 16th-century Mughal palace fort located in Agra, India. It was commissioned by the Mughal emperor Akbar in 1565 and was completed by his son, Jahangir, in 1608. The fort is one of the most popular tourist destinations in India and is a UNESCO World Heritage Site.
The fort is rectangular in shape and is surrounded by a moat. It has four main gates, each of which is decorated with intricate carvings and inlay work. The fort is also home to a number of palaces, mosques, and other buildings.
The Agra Fort is said to possess the unique feature of being exactly equal in length and breath. This is because the fort was built on a square grid, with each side of the fort being the same length. This unique feature makes the Agra Fort one of the most distinctive Mughal buildings in India.
The other options are incorrect because they are not rectangular in shape. The Red Fort is a pentagonal fort, the Taj Mahal is an octagonal tomb, and the Buland Darwaza is a gateway.