In the diagram shown, a plot between $\delta$ (angle of deviation) versus i (angle of incidence) for a triangular prism is given. From the observed plot, some conclusion can be drawn. Mark out the correct conclusion. 

• A

  The range of deviation for which two angles of incidence are possible for same deviation is ${\delta }_0-{\delta }_m$

• B

  The curve is asymmetrical about ${\mathrm{i}}_0$

• C

  For a given $\delta$, i is unique

• D

  Both 1 and 2 are correct.