19. Viscosity is a measure of a fuel’s resistance to flow. The viscosity of a petroleum oil increases when the oil is cooled and decreases when it is heated. The viscosity value of oil must always be associated with the temperature at which the viscosity was determined. Based on these descriptions, which statement is correct?
(A) The oil temperature is not a control parameter of viscosity but the pressure.
(B) The increased temperature reduces the viscosity of oil.
(C) The viscosity value of oil is associated with the temperature at which the oil was sampled.
(D) The viscosity value of oil is associated with the temperature and pressure at which the oil was sampled.