On a hot summer night, the refractive index of air is smallest near the ground and increases with height from the ground when a light beam is directed horizontally , the Huygen's principle leads us to conclude that as it travels, the light beam :

Question

$\begin{array}{1 1} \text{becomes narrower} \\ \text{goes horizontally without any deflection } \\ \text{bends downwards} \\ \text{bends upwards} \end{array} $