Why do people who practise slash and burn agriculture shift to another place after a few years?

The correct option is C The soil becomes infertile
Slash and burn agriculture (Jhum cultivation) is a process of cutting down the vegetation in a particular area, setting that remaining foliage on fire and using the area for cultivation.

Burning provides suitable conditions for upcoming crops because their main competitors like weeds, pests are destroyed and the ash provides nutrients to the soil for planting food crops.

The land burning adds potash to the soil which is like a fertilizer for soil increasing its soil fertility and nutrient content. But continuous burning of the land reduces the amount of moisture and removes the humus (dark, organic material that forms in soil when plant and animal matter decays). Therefore, it affects its fertility. Hence option c is correct.

Slash and burn agriculture is practised on the same plots again and again and farmers move out of the region because the land can not be used for the time being or not at all in the future because of the burning and overcultivation. Leaving the area is not related to any other employment opportunities or services. So option a is incorrect.

Climate is the weather conditions prevailing in an area in general or over a long period. Climate remains constant for a region until a major event happens which changes the climate of the region. Hence option b is incorrect.

Farmers use the same plots or pieces of land again and again along with new areas for expanding agriculture. So expanding agriculture is not the reason for leaving the area. So option d is incorrect.