Which relationship can be selected in a custom report type where Accounts is the primary object and Contacts is the related object?

Which relationship can be selected in a custom report type where Accounts is the primary object and Contacts is the related object?
A . Each contact may or may NOT have a related account.
B . Each contact must have a related account.
C . Each account may or may NOT have related contacts.
D . Each account must NOT have related contacts.

Answer: C