Option 1 suggests that the largest concentration of the peasant population is in areas of intensive shifting cultivation. Shifting cultivation, also known as slash and burn agriculture, involves clearing land and then using it for farming for a few years until the soil fertility declines, at which point farmers move to a new plot of land. While shifting cultivation may be practiced in certain areas of South-East Asia, it does not necessarily mean that there is a large concentration of peasant population in these areas.

Option 2 suggests that the largest concentration of the peasant population is in highland areas where the climate is cooler and healthier. However, there is not enough information provided to support this claim. It is possible that highland areas may have a significant peasant population, but it cannot be stated with certainty.

Option 3 suggests that the largest concentration of the peasant population is in cleared lowlands in forest areas. This option seems plausible as cleared lowlands provide suitable conditions for agriculture and may attract a large peasant population. It is likely that cleared lowlands in forest areas have a significant concentration of peasants.

Option 4, which is the correct answer, suggests that the largest concentration of the peasant population is in areas where grain farming is practiced. Grain farming involves the cultivation of crops such as wheat, rice, and