Which one of the following phenomena is not explained by Huygen's construction of wavefront

A plane wavefront travelling in a straight line in vacuum encounters a medium of refractive index $\mu$. At $P,$ the shape of the wavefront is :

Derive the laws of refraction from the concept (Huygen's principle) of the wavefront. 

By Huygen's wave theory of light, we cannot explain the phenomenon of

The figure shows a surface $XY$ separating two transparent media, medium - $1$ and medium- $2$. The lines $ab$ and $cd$ represent wavefronts of a light wave traveling in medium- $1$ and incident on $XY$. The lines $ef$ and $gh$ represent wavefronts of the light wave in medium- $2$ after refraction.

The phases of the light wave at $c, d, e$ and $f$ are $\phi_c,\phi_d, \phi_e$ and $\phi_f$  respectively. It is given that $\phi_c \neq \phi_f.$

A parallel beam of light strikes a piece of transparent glass having cross section as shown in the figure below. Correct shape of the emergent wavefront will be (figures are schematic and not drawn to scale)-