Which of the following data models is eligible for a NATURAL JOIN?

a$.)$

invoice

invoice$\_$id $*$

total

customer$\_$id $($FK$)$

customer

support$\_$rep$\_$id $*$

name

b$.)$

invoice

invoice$\_$id $*$

total

customer$\_$id $($FK$)$

customer

id $*$

name

c$.)$

invoice

invoice$\_$id $*$

total

cid $($FK$)$

customer

cid $*$

name

d$.)$

invoice

invoice$\_$id $*$

total

id $($FK$)$

customer

customer$\_$id $*$

name