Natural selection occurs only in which of these organizational levels of life?
A. Organ systems
B. Populations
C. Cells
D. Ecosystems

Acts on phenotypes on the individual level but evolution is at the population level. Microevolution is evolution at the population level

Explanation:

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D) Ecosystems

Explanation:

Natural selection is the process whereby organisms better adapted to their environment tend to survive and produce more offspring. Natural selection only applies to ecosystems as ecosystems consist of a whole community of living organisms and their environment. Hope this helps!