\textbf{135-} In an ellipse with semi-major axis $2\sqrt{5}$ and 2 foci, the two foci and the two ends of the minor axis form a square. The sum of the squares of the focal radii of point $M$ on the ellipse is which of the following?
\medskip
(1) $12$ \hfill (2) $16$ \hfill (3) $18$ \hfill (4) $20$
\medskip