((a)) Graduation from a nautical school vessel approved under law and regulation may be substituted for the service requirements under section 7307 or 7314 of this title.
((b)) The satisfactory completion of other courses of instruction approved by the Secretary may be substituted for not more than one-third of the required service on deck at sea under sections 7307–7311 of this title.
((c)) The satisfactory completion of other courses of instruction approved by the Secretary may be substituted for not more than one-half of the required service at sea under .