The Laplace transform of the function $f\left ( t \right )=t^{2}+2t+1$ is $\dfrac{1}{s^{3}}+\dfrac{3}{s^{2}}+\dfrac{1}{s} \\$ $\dfrac{4}{s^{3}}+\dfrac{4}{s^{2}}+\dfrac{1}{s} \\$ $\dfrac{1}{s^{3}}+\dfrac{2}{s^{2}}+\dfrac{1}{s} \\$ $\dfrac{2}{s^{3}}+\dfrac{2}{s^{2}}+\dfrac{1}{s}$

Which one of the following equations represents a one-dimensional wave equation? $\dfrac{\partial u}{\partial t}=C^{2}\dfrac{\partial ^{2}u}{\partial x^{2}} \\$ $\dfrac{\partial ^{2}u}{\partial t^{2}}=C^{2}\dfrac{\partial ^{2}u}{\partial x^{2}} \\$ ... $\dfrac{\partial ^{2}u}{\partial t^{2}}+\dfrac{\partial ^{2}u}{\partial x^{2}}=0$

Protein concentration of a crude enzyme preparation was $10\:mg\:mL^{-1}$. $10\:\mu L$ of this sample gave an activity of $5\:\mu mol\:min^{-1}$ under standard assay conditions. The specific activity of this crude enzyme preparation is ____________ units $mg^{-1}$.