Are areas around the world that support similar communities of species, and are smaller, local communities within these areas.
a. biomes . . ecosystems
b. elevations . . biomes
c. biomes . . elevations
d. ecosystems . . climates

a. Biomes . . . ecosystems

Explanation:

A biome is the region which includes the communities of living beings such as plants and animals. These are found in the range of the continents. The organisms living in a particular biome shows the characteristics typical to the biome and adaptations specific to the biome. Biomes becomes different on the basis of the physical climatic conditions specific to them.

The ecosystem is the communities of the species found in the biome. There are many ecosystems in the single biome.

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i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.