The "domicile" of an insurer means:
a. As to Canadian insurers, the province in which the insurer's head office is located.
b. As to other alien insurers authorized to transact insurance in one or more States, as provided in section 17B:23-5c.
c. As to alien insurers not authorized to transact insurance in one or more States, the country under the laws of which the insurer was formed.
d. As to all other insurers, the State under the laws of which the insurer was formed.