The correct answer is C) the foundation of Buddhism.
The achievement that is attributed to India during the classical era is the foundation of Buddhism.
In the 3rd century BC. the Mauryan Indian Emperor Ashoka the Great, established Buddhism as the official religion in the empire. That is when he ordered the construction of many temples to pray and supported the spread of Buddhist teaching across the empire. Years later, Buddhism spread to other regions and territories due to trade, basically during the Silk Road trade routes.
