Fuel injection pumps using the port and helix metering principle requires the use of a __________.

Correct Answer: Option B — lapped plunger and barrel

Port and helix fuel injection pumps rely on extremely tight manufacturing tolerances between the plunger and barrel, typically measured in microns. This lapped fit prevents high-pressure fuel bypass without needing traditional piston rings, ensuring precise volumetric metering under extreme pressures mandated by marine diesel operating principles.