Given the tables in our example database in Section $1$ of the tutorial, if an existing employee wanted to add a new customer and put in an invoice, in what order should the table data be inserted?

a$.)$

invoice$\_$line

invoice

customer

b$.)$

employee

customer

invoice

invoice$\_$line

c$.)$

invoice$\_$line

invoice

customer

employee

d$.)$

customer

invoice

invoice$\_$line