In the visible region, the dispersive powers and the mean angular deviations for crown and flint glass prisms are $\omega, \omega^{\prime}$ and $d, d^{\prime}$ respectively. The condition for obtaining dispersion without deviation, when the two prisms are combined, is:

• A
  $d + d^{\prime} = 0$
• B
  $\omega^{\prime} d + \omega d^{\prime} = 0$
• C
  $\omega d + \omega^{\prime} d^{\prime} = 0$
• D
  $\omega d^2 + \omega^{\prime} d^{\prime 2} = 0$