The correct answer is - A. The Russian serf system arose as peasants fled to the protection of large landowners to avoid Mongol taxes.
After the Mongol invasion of Russia, the people were understandably scared, both for their own safety and because of economic reasons, as the Mongols demanded taxes which were seen by the Russian as too big.
That resulted in many people fleeing to the large landowners. The purpose of this was that they would have worked for the owners, and would have been controlled, as well as pay a certain amount of money or in products, but they had protection. The safety issue in this way was largely solved, and the taxes were lower, so the people entered into the world of the serfdom.
