Question Stem
The claims above, if true, most strongly support which of the following conclusions?
Inference Question. So the answer MUST BE TRUE.

Argument
For a trade embargo against a particular country to succeed, a high degree of both international accord and ability to prevent goods from entering or leaving that country must be sustained. A total blockade of Patria's ports is necessary to an embargo, but such an action would be likely to cause international discord over the embargo.

My Understanding of the Argument
Successful Trade Embargo needs both 1) high degree of international accord 2) ability to prevent goods from entering or leaving that country.
BUT blocking Paricia's ports is likely to cause international discord over the embargo.

Pre-thinking
Embargo may not be successful in Patricia

Answer Choices
(A) The balance of opinion is likely to favor Patria in the event of a blockade
INCORRECT ANSWER - Whether the balance of opinion will favor or not favor is not discussed in the passage. Out of Scope

(B) As long as international opinion is unanimously against Patria, a trade embargo is likely to succeed.
INCORRECT ANSWER - Two conditions are necessary for an embargo. In this option, nothing about the condition 2 (ability to prevent goods from entering or leaving that country) is mentioned

(C) A naval blockade of Patria's ports would ensure that no goods enter or leave Patria.
INCORRECT ANSWER - Not Sure if sea is only way in which goods enter Patricia . Goods could enter the country through other routes as well. We can not say that this is true.

(D) Any trade embargo against Patria would be likely to fail at some time.
CORRECT ANSWER - As the trade blockade would like to cause international discord (which is condition 1 for an embargo to be successful), there is a likelihood that the embargo will fail at some point in time

(E) For a blockade of Patria's ports to be successful, international opinion must be unanimous.
INCORRECT ANSWER - "unanimous" - nothing mentioned. May be a majority would do. The passage does not lead us to believe this option