How do the Upanishads challenge the caste system?

Historically, the most important of the Upanishads are the two oldest, ... Challenges to Brahmanism (6th–2nd century bce) ... The Atharvaveda describes another class of religious adepts, or specialists, the vratyas, particularly ... hierophant (one who manifested the holy) who remained outside the system of Vedic religion.

Explanation:

b) to encourage free trade

one way archaeology us understand the past is through the material objects it finds, allowing us to know what was being used, and when. for example a dig recently found a flute, believed to be the oldest musical instrument found to date.

i hope this