In Fig. $33-47 a,$ a light ray in an underlying material is incident at angle $\theta_{1}$ on a boundary with water, and some of the light refracts into the water. There are two choices of underlying material. For each, the angle of refraction $\theta_{2}$ versus the incident angle $\theta_{1}$ is given in Fig. $33-47 b$. The horizontal axis scale is set by $\theta_{1 y}=90^{\circ} .$ Without calculation, determine whether the index of refraction of (a) material 1 and (b) material 2 is greater or less than the index of water $(n=1.33) .$ What is the index of refraction of (c) material 1 and (d) material $2 ?$