The united states disagrees with a government of a foreign country. so it imposes a(n) on trade between the two countries.
standard
subsidy
embargo

The answer is embargo.

Standard- Normal
Subsidy- Form of financial aid.
Embargo- Impose a ban on trade on a country.

And if you disagree with a country, you're more likely to embargo them rather than subsidy them and standard pretty much makes no sense in the sentence.