In the diagram, a sector of a circle has central angle 120^{\circ}. The area of the whole circle is 9 \pi. What is the area of this sector?

Answer Choices
A. 2 \pi
B. 3 \pi
C. 4 \pi
D. 6 \pi
E. \frac{9}{2} \pi
In the diagram, a sector of a circle has central angle 120^{\circ}. The area of the whole circle is 9 \pi. What is the area of this sector?
Answer Choices
A. 2 \pi
B. 3 \pi
C. 4 \pi
D. 6 \pi
E. \frac{9}{2} \pi