They started domesticating wheat. This wasn't their main feat however since they also started herding sheep and domesticating goats. These two enabled them to stop moving around like nomads and make a real civilization in the area which resulted in what is now known as history.
When the previous inhabitants of the Indus Valley moved to India, they encountered people from central Asia. These people brought their own religion and customs, including their religion, Vedism. Archaeologists believe that this religion combined with that of the Indus Valley to create what is now known as Hinduism<span>.</span>
Usually, back then, they followed their food and tracked them without settling too long in one place. But since that's not one of the answers I would go with A.
I hope that helps.
