Upanishad
These texts developed after the composition of the core Vedas and provided further insights into Hindu philosophy and spirituality.
The Early UpanishadsThese are a group of Hindu scriptures that date back to around 800-400 BCE and are considered the foundation of Hindu philosophy. Some of the most well-known early Upanishads include:
Brihadaranyaka Upanishad
Chandogya Upanishad
Taittiriya Upanishad
Aitareya Upanishad
Katha Upanishad etc.
These texts contain spiritual teachings and discussions of the nature of reality, the self, and ultimate reality (Brahman).
The First Stupa
The first stupa is believed to have been built by the Indian Emperor Ashoka in the 3rd century BCE. Stupas are dome-shaped structures that were originally used to house Buddhist relics and were used as places of pilgrimage and meditation.
The Great Stupa at Sanchi, located in central India, is one of the earliest and best-preserved examples of Ashoka's stupas and is considered a landmark in the development of Buddhist architecture. It is said to contain the ashes of the Buddha and other important Buddhist relics, and it was a major center of Buddhist pilgrimage in ancient times.
Mahayana Buddhism
It is one of the major branches of Buddhism and is characterized by its emphasis on the bodhisattva ideal and the concept of emptiness (shunyata). It originated in India around the 1st century CE and spread to other parts of Asia, including China, Japan, and Korea.
Earliest Temples
​The temple architecture in India developed around the 4th century BC during the Gupta period. The Gupta period witnessed rock-carved deity in Hindy art. The Gupta rulers were not pleased with caves, so they decided to build free-standing structures known as temples."

So, the correct option is [2]