A thin prism P with angle `4^(@)` and made from glass of refractive index 1.54 is combined with another thin prism P made from glass of refractive index 1.72 to produce dispersion without deviation The angle of prism P is
A. `delta_(m)=r`
B. `delta_(m)=1.5r`
C. `delta_(m)=2r`
D. `delta_(m)=r/2`