Discussion

Explanation:

Thwart means ‘frustrate, ruin, or stop’. Where it means ‘stop’, it may still be applicable. ‘Close’ an argument is also an option. ‘Defeat (option 3)’ can be easily eliminated. The best alternative here is ‘resolve’. But resolve fits in best with the sentence as one resolves or solves an argument.
Hence, the correct answer is option 1.

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