If $ a = \large\frac{2 - \sqrt 5}{2+\sqrt 5},$$b = \large\frac{2+\sqrt 5}{2- \sqrt 5}$ then $a^2 -b^2 =$

Question

$\begin{array}{1 1} 144\sqrt 5 \\ -144 \sqrt 5 \\ 60 \\ -60 \end{array} $