What must be entered, after the Shore I.D. and "#" sign is entered and a ring-back tone is heard, to obtain the assistance of the national telephone operator in the Inmarsat-B service?

Correct Answer: Option D — 13#

The sequence 13# is the designated Inmarsat-B service code for accessing the national telephone operator of the country where the Land Earth Station is located. This allows the vessel to request assistance specific to the local telecommunications infrastructure after the initial connection is established via the Shore I.D.