Why Are Deserts and Tundra Among the Least Productive Terrestrial

Why are deserts and tundra among the least productive terrestrial biomes?

A) Water is not easily accessible by plants in desert and tundra biomes, and both of these biomes experience extreme temperature conditions. Water availability and temperature are important limiting factors in net primary productivity (NPP) .
B) There is too much water available in the tundra and not enough available in the desert. The extreme temperatures of these biomes do not affect NPP.
C) There is not enough sunlight available in either the tundra or the desert biomes to sufficiently support NPP.
D) There is far too much sunlight and water available in both the desert and tundra biomes. These factors cause photosynthesis to be suspended and result in dramatically decreased NPP.