What does it mean that the genetic code is "highly conserved"?

What does it mean that the genetic code is "highly conserved"?​

a.​it resists modification from environmental mutagens

b.​the products of the genetic code - proteins - are almost the same in all organisms

c.​it is almost universal and has not changed in millions of years

d.​all organisms and organelles - without exception - have the exact same genetic code

e.​organisms can only use it a certain number of times