The correct answer is: [B]: "decreased" .
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Note:
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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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