The radius of an air bubble is increasing at the rate of $\large\frac{1}{2}$ cm/s. At what rate is the volume of the bubble increasing when the radius is $1\; cm$?

Question

$\begin{array}{1 1} (A)\;\large\frac{1}{2\pi}cm^3/s \\ (B)\;\large\frac{-1}{2\pi}cm^3/s \\ (C)\;-2 \; cm^3/s \\ (D)\;2\pi \; cm^3/s \end{array}$