The Surface Area of a Right Circular Cylinder of Height $S = \pi r ^ { 2 } + 18 \pi r$

Multiple Choice

The surface area of a right circular cylinder of height 9 units is given by $S = \pi r ^ { 2 } + 18 \pi r$ . Factor this expression.

A) $r ^ { 2 } ( \pi + 18 r )$
B) $r ( r + 18 \pi )$
C) $\pi r ( r + 18 )$
D) $r ^ { 2 } ( \pi + 18 )$
E) $\pi \left( r ^ { 2 } + 18 \right)$