Which of these two influences did the Aryans bring to Indian society?

Irrigation and Sanskrit

Caste system and Buddhism

Caste system and Hinduism

Military supremacy and art

The aryans broght a completely new language and belief system to India. We see a dramatic discontinuity between the Indus valley civilization (4000BC-2000BC) which buried its dead and had a script which is still not deciphered and the vedic period which spoke sanskrit (the world's oldest indo European language) and cremated their dead. They also brought in the caste system (though this is political dynamite in India so you are advised to avoid this topic) as well as vedic gods and practices and concepts such as transmigration of the soul, reincarnation etc which are still the pillars on which all dharmic faiths of India are built on and then later spread to the rest of Asia via Buddhism.