Assume you want to write a recursive function that multiplies each element in a list by the number $5.$ What should the base case be$?$ Please choose from the following options:

a$)$ When the length of the list is $1$

b$)$ When the length of the list is $0$

c$)$ When the list is equal to $1$

d$)$ When the list is equal to $0$

Thank you