How to create new variable but not a link to old variable?

Question

I tried to create 3 new variables b,c,d based on a:

a = [1,2,3,4,5,6,7,8,9]
b = a
c = b
d = c

but when I do this:

d[4]=5000
print(a)

It doesn't print the original a but d.

How can I print the original a?

Thanks.