Explanation

The sentence describes a relationship between imperial metropoles and their colonies characterized by "irreconcilable opposition" where one side's gains come at the direct expense of the other (a zero-sum game).

Adversarial and Antagonistic both mean showing opposition, hostility, or conflict, which perfectly mirrors the phrase "irreconcilable opposition."

Both words fit the blank grammatically and contextually, creating two sentences that are identical in meaning.

B. exploitative and C. mercenary make sense contextually when talking about colonialism, but they do not have a matching synonym pair among the choices that maintains the specific meaning of "irreconcilable opposition."

E. variable and F. changeable directly contradict the idea that this dynamic was a "structural necessity" rather than a "contingent historical accident."

Answer: A,D