A ladder 5 m long is leaning against a wall. The bottom of the ladder is pulled along the ground, away from the wall, at the rate of 2cm/s. How fast is its height on the wall decreasing when the foot of the ladder is 4 m away from the wall ?

Question

$\begin{array}{1 1}(A) \;\frac{8}{3}cm/s \\ (B)\frac{-8}{3}cm/s \\ (C)\;\frac{8}{3}cm^2/s \\ (D)\;\frac{8}{3}cm^2/s \end{array} $