Which one of the following devices relies on gravity to infuse the solution?

A. PCA device: A patient-controlled analgesia (PCA) device uses programmed electronic controls to deliver medication, not gravity, to ensure precise dosing and timing. B. infusion pump: An infusion pump actively controls and delivers fluids at a set rate using mechanical force, independent of gravity. C. syringe pump: Syringe pumps use motorized pressure to deliver fluids in small volumes over time and do not depend on gravitational flow. D. rate controller: A rate controller works with gravity by regulating the flow of IV fluid from the bag into the patient using a dial or clamp but does not apply mechanical force itself.