There are four layers of glass plates, placed on top of each other...

There are four layers of glass plates, placed on top of each other such that bottom one has thickness $\mathrm{a}_1$ and refractive index $\mathrm{n}_1=2.7$. Next one has thickness $\mathrm{a}_2$ and refractive index $\mathrm{n}_2=2.43$. The third one and the top one have thickness $\mathrm{a}_3$ and $\mathrm{a}_4$ and refractive indices $\mathrm{n}_3$ and $\mathrm{n}_4$ respectively. Three rays starting at the same moment from $\mathrm{A}_1, \mathrm{~A}_2$ and $\mathrm{A}_3$ reach points $\mathrm{B}_2, \mathrm{~B}_3, \mathrm{~B}_4$ at the same time, with their angles of incidence being critical angle. You are given $A_1 B_1=A_2 B_2=A_3 B_3=A_4 B_4=b=10 \mathrm{~mm}$. Choose correct statement (s).