The answer is A if you have any more questions let me know
Survival of the fittest is another way to describe the roll it plays seeing as that the organisms best fitted to survive an area will and can produce more of the fittest species; the ones who are best fit will die
I believe the answer to this is D.

The greenhouse effect is a natural process that warms the Earth's surface. When the Sun's energy reaches the Earth's atmosphere, some of it is reflected back to space and the rest is absorbed and re-radiated by greenhouse gases. The absorbed energy warms the atmosphere and the surface of the Earth.
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- The integumentary system is the answer. It consists of the skin , hair, nails, glands and nerves.