The velocity of light in a glass fiber of refractive index 1.5 is —

• a$3 \times 10^8$ ms⁻¹
• b$2.66 \times 10^8$ ms⁻¹
• c$2 \times 10^8$ ms⁻¹
• d$1.5 \times 10^8$ ms⁻¹