What is the main factor that separates the biomes?

Terrestrial biomes are distinguished primarily by their predominant vegetation, and are mainly determined by temperature and rainfall. Differences in temperature or precipitation determine the types of plants that grow in a given area .

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.