Oxygen, neccessary for cellular respiration, is the answer. As oxygen becomes scarce, your cells begin to aerobically produce very little ATP, in effect fermenting and producing lactic acid.
The correct answer is: [B]: "decreased" .
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<u>Note</u>:
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In a graph of "coal reserves in the United States" vs. "time" ;
→ the "time" is the "independent variable" that belongs on the "x-axis" .
→ The quantity or amount of "coal reserves in the United States" is the "dependent variable" that belongs on the "y-axis" .
If the graph "slopes downward" ; this would indicate a "decrease" in the amount/quantity of "coal reserves" over "time" .
→ As the value of "x" increases — "time" increases — and; as "x" increases, the value of "y" {the amount/quantity of "coal reserves"} decreases.
→ This would be represented by a "downward sloping" graph;
→ and, among the answer choices given, could indicate that coal production:
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→ "decreased" ;
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→ which is: Answer choice: [B]: "decreased" .
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natural selection, bc it is the process whereby organisms better adapted to their environment tend to survive and produce more offspring