# Two periodic waves of intensities $I_1 \: and \: I_2$ pass through a region at the same time in the same direction. The sum of the maximum and minimum intensities is :

$\begin {array} {1 1} (1)\;2(I_1+I_2) & \quad (2)\;I_1 + I_2 \\ (3)\;( \sqrt{I_1}+ \sqrt{I_2} )^2 & \quad (4)\;( \sqrt{I_1}- \sqrt{I_2} )^2 \end {array}$