I think the answer is B.
Because one of the factors that has prevented it from being a more unified country is its geography. It's rugged, mountainous. It's very difficult for any invading army to develop or control it.
I personally believe that the right answer is C. Other overpopulation results in more living organisms, and since the pollution has intoxicated the living, they die releasing the carbon into the soil. So there is high amounts of carbon and less of the organic compounds because the overdose on carbon.
Substinence farming is farming food that is just enough to live off of. You don't sell substinence crops.
Commercial farming is growing food to sustain you, and having enough left over to sell.
In both, you grow food and you keep some (or all) for yourself.
