$\sqrt {12-\sqrt {68+48 {\sqrt {2}}}}$ is equal to :

Question

$$\begin {array} {1 1} (a)\;\sqrt 2-3 & \quad (b)\;2+\sqrt 2 \\ (c)\;2 - \sqrt 2 & \quad (d)\;6-2 \sqrt 8 \end {array}$$