Why do you think we have different Biomes in the world? Why don't we just have one Biome the
same throughout the world?

Each biome has a unique set of environmental conditions and plants and animals that have adapted to those conditions. The major land biomes have names like tropical rainforest, grasslands, desert, temperate deciduous forest, taiga (also called coniferous or boreal forest), and tundra.

Explanation:

A biome is different from an ecosystem. An ecosystem is the interaction of living and nonliving things in an environment. A biome is a specific geographic area notable for the species living there. A biome can be made up of many ecosystems. For example, an aquatic biome can contain ecosystems such as coral reefs and kelp forests.

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.