[填空题]
vA piece of material,pijm a7+9f.( hu5u6.f dpke( 6ebmfc x suspected of being a stole-x;c() tjx vf.c,cyqtn diamond $(n=2.42)$ is submerged in oil of refractive index 1.43 and illuminated by unpolarized light. It is found that the reflected light is completely polarized at an angle of 59$^{\circ}\,$. Is it diamond?
