What statement is true concerning the arrangement and operation of the viscosity sensor as used for sensing the viscosity of heavy fuel oil?

Correct Answer: Option D — The viscosity sensor is fitted with a constant speed fixed capacity pump and a capillary tube which produces a pressure drop at constant flow which is proportional to the oil viscosity.

Viscosity sensors utilize a constant speed, fixed-capacity pump to force oil through a capillary tube. Because the flow rate remains constant, the pressure drop across the capillary is directly proportional to the oil's viscosity, allowing the system to accurately control fuel preheating temperatures for optimal combustion in marine engines.