The correct answer is A. the soil is frozen and devoid of nutrients
Tundra's land is formed from ice and from cold weather, meaning that there's no nutrients since the land is basically frozen wasteland.
'Climatic variations' and 'Human activities' can be regarded as the two main causes of desertification. removal of the natural vegetation cover（by taking too much fuel wood）, agricultural activities in the vulnerable ecosystems of arid and semi-arid areas, which are thus strained beyond their capacity.
Biomass is organic material which has stored sunlight in the form of chemical energy.
When dead body parts decay.
