When an Oil Well Burns, Sediment Is Carried Up into the Air

Multiple Choice

When an oil well burns, sediment is carried up into the air by the flames and is eventually deposited on the ground.Less sediment is deposited further away from the oil well.Suppose that the density (in tons/square mile) at a distance r from the burning oil well is given by $\frac{9}{1+r^{2}}$ .Which Riemann sum approximates the total amount of sediment which is deposited within 100 miles of the well?

A) $\sum \frac{9 \pi r^{2} \Delta r}{1+r^{2}}$
B) $\sum \frac{18 \pi r^{2} \Delta r}{1+r^{2}}$
C) $\sum \frac{18 \pi r \Delta r}{1+r^{2}}$
D) $\sum \frac{9 \pi r \Delta r}{1+r^{2}}$