Answer:
Option A.
Step-by-step explanation:
It is given that a graph of coal reserves in the united states versus time slopes downward.
It means, in the graph x-axis represents the time and y-axis represents the coal reserves.
Negative slope represents the negative relation between coal reserves and time. It means coal reserves will decrease if time increases.
In other words, the downward slope indicates that coal production could have decreased.
Therefore, the correct option is A.