The three-field system was an agricultural policy which divided the land of a state into 3 categories. One third was planted in autumn with rye or wheat. The second was planted with the remainder available crops such as beans or peas. The third was left unplanted.
This system allowed farmers to increase their production as cereal crops depleted the land of nitrogen due to their excessive consumption but the legumes converted the nitrogen in the air into ammonia which fertilized the soil. The third field was soon overgrown with weeds that were used for grazing animals.
Answer: A. A historian analyzes dozens of primary sources to reach a
conclusion about the effects of the Cold War on Russian politics.
In order for a historian to arrive at an objective view, it is necessary to analyze multiple sources in order to form a scientific view. In this context, it is necessary to analyze a larger number of historical sources because only in this way can historical truth be reached. The analysis of one or two sources is insufficient, since in order to create a broader context, it is necessary to support all available sources with scientific analysis.