Let's go through the process of elimination.
it can't be A, they are constantly making trades and it is a notably rich place.
it can't be C, it is extremely big, and, as i said, always trading with NEIGHBORING Countries.
it can't be D, since they are a noticeably peaceful and happy Country. The last war they were in was in 2011, i believe.
Our answer is B
(no source)
