Darwin's argument tells us that species develop their traits through natural selection due to competition, survival and reproduction. Diversification of species is an important part to make his argument valid because diversification suggest extinction of specie if it doesn't survive.
Answer:
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D. Happiness leads to great success
Explanation: D. Happiness leads to great success
A, In Fact, studies by scientists have found......
In fact followed up by an actual factually proven statement!