7. Why is it necessary for water, carbon, oxygen and nitrogen to be recycled through Earth's ecosystem?
A. The ecosystem would be polluted
B. It is just the way of natural ecosystem C. We would not be able to survive due to too much of Carbon in the atmosphere D. So that the materials will be used up and become available again for living organism
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Answer:
letter D. so that the materials will be used up and become available again for living organisms