Answer:
are caused by genes carried on the X and Y chromosomes
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Answer:
Fossil fuels are hydrocarbons, primarily coal, fuel oil or natural gas, formed from the remains of dead plants and animals. In common dialogue, the term fossil fuel also includes hydrocarbon-containing natural resources that are not derived from animal or plant sources.
Answer: There must be diseases and natural disasters present in an ecosystem.
Explanation: The other two answers must be present for it to be natural selection.