The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
Considerable social change took place in the subcontinent from the 11th-12th century onwards. Varna-based society and tribal people constantly interacted with each other. This interaction caused both kinds of societies to adapt and change. There were many different tribes and they took up diverse livelihoods. Over a period of time, many of them merged with caste based society. Others, however, rejected both the caste system and orthodox Hinduism. Some tribes established well-organised systems of administration. They thus became politically powerful. This brought them into conflict with larger and more complex kingdoms and empires.