In a right angled triangle $ABC$, where $\angle B = 90^{\circ}$, if $\angle A = 30^{\circ}$ and $AB = 4 \;cm$. <br> What is the length of $BC$ ?

Question

$\begin{array}{1 1} (a)\;\frac{4}{3} \\ (b)\; \frac{4\sqrt{3}}{3} \\ (c)\; 4 \\ (d)\; 3 \end{array}$