Answer: A) The country that currently buys most of Zeria's exports recently suggested that it might severely restrict its imports from Zeria unless Zeria broke off diplomatic relations with Nandalo.
Step-by-step explanation:
When countries a lot of the times, there is usually an ulterior motive to it and this often comes down to money. In this case, keeping relations with Nandalo must have somehow threatened the money supply to Zeria and so Zeria had to take action against this.
Option A provides a plausible reason as to why this could be the case. If a country that buys a lot of Zeria's exports threatens to stop buying from Zeria, they would be inclined to act in a way that the country wants in order for the country to keep buying those exports and if that includes breaking off relations with Nandalo then it will be done.