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
  $\phi_c$ cannot be equal to $\phi_d$
• B
  $\phi_d$ can be equal to $\phi_e$
• C
  $(\phi_d - \phi_f) = (\phi_c - \phi_e)$
• D
  $(\phi_d - \phi_c) \neq (\phi_f - \phi_e)$