Answer:
I think also that is b.
a "cascada" is a waterfall
an "ecosistema" it's an ecosistem
a "glaciar" it's a glacial
a "llanura" it's an evenness.
So I think that the best option its an ecosistem, because it have plants and animals.
Explanation:
The correct option to fill the sentence in Spanish is:
An ecosystem is considered to be any environment that allows its biotic components, such as animals and plants, and abiotic components to coexist and interact with each other, giving rise to a community within a given environment.
Rivers can be considered a fairly complete ecosystem since they have different types of fish and aquatic plants, as well as abiotic components such as rocks, beds, water, among others.
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