Biotic factors are the living things that determine an ecosystem. So by knowing that, we can eliminate B and D. And between A and C, A is correct. Deciduous forest biomes can be found in the eastrn half of United States, and I'm positive that you have never heard elephants and giraffes being native to US. And the only place to see those animals are in zoos where they are shipped from their homeland. So, once again, the answer is A.
