Prohibitively high tariffs on salmon. . .

[Vincen]

Prohibitively high tariffs on salmon from Winterland allow companies in the Republic of Osum to sell salmon without any foreign competition. Some economists believe that the tariffs partly explain why Osum salmon costs one dollar more than Winterland's salmon. If the government removed the tariffs, consumers would either purchase more Winterland salmon than they would Osum salmon or else Osum companies would have to reduce the price of their salmon.

The conclusion reached in the last sentence depends upon which of the following assumptions?

A) The legislature of Osum proposes tariffs and the Prime Minister ratifies them.
B) Winterland has passed a countervailing tariff against salmon from the Republic of Osum.
C) A constitutional amendment is not needed to remove the tariffs.
D) Although the Republic of Osum has lower tariffs on salmon from other countries besides Winterland, these tariffs are just as effective in eliminating all salmon imports.
E) Osum salmon is not over one dollar better in quality than is Winterland salmon.

The OA is E.

What is the best approach to solve this CR question?