The book of Obadiah prophesies primarily against which nation, highlighting a specific sin that led to their condemnation?

A Babylon, for their idolatry and oppression of Israel. B Assyria, for their military aggression and cruelty. C Edom, for their gloating and taking advantage of Judah's distress during its downfall. D Egypt, for their false gods and enslavement of the Israelites.