Answer:
The correct option is c.
Explanation:
We need to find a graph which is the most appropriate to describe a quantity decreasing at a steady rate.
Quantity decreasing at a steady rate means the quantity decreasing at constant rate.
If a function decreases by a constant value, then the graph of function is a straight line with a downward slope.
Only graph c represents a straight line with a downward slope.
Therefore the correct option is c.