Here is my reasoning.
Conclusion: Therefore, it is wrong for any country to adopt trade policies that are likely to seriously hinder growth in the prosperity of any other country.
This is a judgement that the negotiator is passing that
IT IS WRONG to adopt trade policies which have the probability of hindering growth for the other country.
If we notice this judgement, it sounds STRONG.
(A)- Every country should adopt
at least some policies that encourage the development of political freedom in other countries.
This means at least some policies should support the growth, which also means that there may be some policies that do not support. But our conclusion is strongly saying it is wrong to have a negative policy only. Therefore it is wrong.
(B)- Overall well being is out of scope.
(C)- Why a country seeks economic prosperity is irrelevant to the conclusion.
(E)- Conclusion is concerned about other countries option is about our country. Clearly, going in wrong direction.
This lefts us with D
Notice how strong this option looks like and it perfectly aligns with our strong conclusion.
Hope it makes sense.
Let me know in case of any doubt.