Read the passage and answer the following question:

The tradition of erecting stupas may have been pre-Buddhist, but they came to be associated with Buddhism. Since they contained relics regarded as sacred, the entire stupa came to be venerated as an emblem of both the Buddha and Buddhism... Asoka distributed portions of Buddha's rehes to every important town and ordered the construction of stupas over them. By the 2nd century BCE, a number of stupas, including those at Bhuhut, Sanchi and Sarnath had been built.

Why did the entire stupa came to be venerated as an emblem of both the Buddha and Buddhism?

They contained relics.

The correct answer is Option (3) → They contained relics. 

Relics of the Buddha: Stupas were built to house the physical remains of the Buddha, such as bone fragments or ashes. These relics were considered sacred because they were associated with the Buddha's physical form and his enlightened state. The presence of relics made the stupas significant spiritual focal points.

Symbolism of Enlightenment: The construction and veneration of stupas symbolize the enlightenment and spiritual legacy of the Buddha. Stupas, with their architectural elements like the dome and spire, represent the cosmic axis and the journey from the material world to the spiritual realm.

Pilgrimage Sites: Stupas became important pilgrimage sites for Buddhists. Pilgrims visited these stupas to pay homage to the relics and to seek spiritual merit. The act of circumambulating the stupa, called pradakshina, is a common practice during pilgrimage and symbolizes the path to enlightenment.

Spread of Buddhism: As Buddhism spread across different regions, the construction of stupas became a means of propagating the Buddha's teachings. Stupas served as visible symbols of Buddhism, attracting devotees and fostering a sense of community and religious identity.

So, the correct option is [3].