Which of the following is a correctly formatted Inmarsat-C address book entry for sending communications to a fax machine on a vessel in the IOR?

Correct Answer: Option D — 8731509987

Ship-to-ship Inmarsat-C addressing requires the ocean region prefix followed by the vessel's 9-digit identification number. The IOR region is designated by the prefix 873. Therefore, 8731509987 is the correct format, as it correctly identifies the satellite region and the specific mobile terminal being addressed for the fax transmission.