The correct answer is - influence of Muslim culture.
The Taj Mahal is one of the greatest architectural achievements of the Mughal Empire in India, and it is in perfectly good shape even nowadays. It is a very nice example of the Muslim influence in India, as the structure itself is a complex mixture of Islamic architecture, with Persian and Turkic elements, made in great detail.
The Taj Mahal is a very beautiful structure, but the reason behind its building is a sad one, as it was built by a Mughal Emperor in order to honor his beloved wife that died very young.