Answer: Some organs such as the heart, kidneys, liver, lungs and eyes perform vital functions, cannot be easily replaced, and when donated can save lives or restore sight of other persons; hence they are most valuable.
The heart pumps blood, the kidneys filter wastes from blood, the liver carries out many metabolic functions and the eyes give vision. Failure of the heart, liver or both kidneys endangers life; loss of eyes causes blindness. For many patients with such organ failure the best treatment is transplantation of a healthy organ from a donor (for kidney failure, dialysis can support the patient only for some time).
Organs like a kidney can be donated during life, while the heart, liver and eyes can be donated after death. Organ donation can save the lives of many needy persons and blind persons can regain vision. Hence these organs are most valuable, and we should take care of them and pledge to donate them.