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 relics to every important town and ordered the construction of stupas over them. By the 2nd century BCE, a number of stupas, including those at Bharhut, 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.

As per the passage:

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 relics to every important town and ordered the construction of stupas over them. By the 2nd century BCE, a number of stupas, including those at Bharhut, Sanchi and Sarnath had been built.