If m is the A.M of two distinct real number l and n (l,n >1) and $G_1,G_2$ and $G_3$ are three geometric means between l and n, then $G_1^4 +2 G_2^4+G_3^4$ equals

Question

$\begin{array}{1 1} 4lA^2m^2n^2 \\ 4l^2mn \\ 4lm^2n \\ 4lmn^2 \end{array} $