A specific purpose gives one a motivation for a cause, while a central idea gives one the broader picture of how this specific purpose can have a positive or negative impact on society, business, or family.
I think that the best answer to this is foreign investment: it was the one aspect which has helped Bulgarian economy the most.
The foreign investment is mostly connected to tourism - especially for example when rich western Europeans buy property in Bulgaria for private use.
The earliest event from these was:
753 BCE: City of Rome founded
Then this happened:
509 BCE: Roman republic founded
Then:
27 BCE: Roman Empire established
After which:
410 CE: Alaric seized Rome
And finally:
476 CE: Odoacer sacked Rome
You can figure out the chronological order by looking if it has either CE or BCE - BCE is before Christ and CE is after Christ. When counting from BCE it goes from higher numbers towards zero. When counting from CE it goes from zero to higher numbers again.
Answer:
I am not completely sure, but I would go with A
The land was on a gold mine
