Critical Reasoning

Commentator: The theory of trade retaliation states that countries closed out of any of another country's markets should close some of their own markets to the other country in order to pressure the other country to reopen its markets. If every country acted according to this theory, no country would trade with any other.

The commentator's argument relies on which of the following assumptions?

(A) No country actually acts according to the theory of trade retaliation.
(B) No country should block any of its markets to foreign trade.
(C) Trade disputes should be settled by internation tribunal.
(D) For any two countries, at least one has some marked closed to the other.
(E) Countries close their markets to foreigners to protect domestic producers.

This Q confused me a lot.
Conclusion: If every country acted according to trade retaliation theory, no country would trade with any other.

Based on conclusion i selected A. But OA is D. Is my conclusion correct?

When you see options with No: Kindly convert the question to "weaken" for a trial run and negate the options.

Modified A) Countries actually act according to theory of trade retalliation.
This has to weaken the conclusion but it provides one more premise and strenghten the conclusion that no trade happens with one another.

I hope my approach is correct