Answer:
B, the ability to determine its own nationally-oriented monetary policy.
Step-by-step explanation:
When a country merges its currency with another to form/create a single currency, the nation must give up its ability to make monetary policies with the country.
This is because the creation of a single currency has now joined both countries as one monetarily. For this reason, both nations have to come to an agreement on monetary policies that will apply in both country as soon as there is a currency merger.
Cheers.