What is the difference between graded index and step index multi$-$mode fiber?

a$.$

Step index has a larger core than graded index.

b$.$

Graded index has a gradual change in the refractive index of the core, while step index has no change.

c$.$

Graded index has more light dispersion than step index.

d$.$

Graded index is more commonly used than step index.

select all that applies