The prophecy in Obadiah primarily concerns judgement against which nation, and what was the root cause of their condemnation?

A Babylon, for their destruction of the Temple in Jerusalem and enslavement of the Israelites. B Egypt, for their idolatry and oppression of the Israelites during their time in slavery. C Edom, for their gloating and opportunistic violence against Judah during its distress and vulnerability. D Assyria, for their brutal conquest and exile of the Northern Kingdom of Israel.