I believe the correct answer is B. The abiotic factor in a desert would be the sand. Abiotic factors are components that are non-living in an environment that would have an effect of the organisms and the whole ecosystem. Examples of abiotic factors are rain, temperature, soil, pollution, pH, altitude and wind. The opposite of this is called the biotic factors which are the living components in the ecosystem. Both are associated with each other and when one factor would change, it would affect the whole system. Abiotic factors are very important since they would affect directly the survival of the living organisms in the system.
