Analysis of test questions: blood donation without compensation refers to the act of selflessly dedicating one's blood to social welfare undertakings in order to save others' lives. Blood donors do not receive any remuneration from blood collection units and blood donors. The age of encouraging voluntary blood donation in China is 18-55 years old, with males weighing more than 50 kg and females weighing more than 45 kg. Those who pass the physical examination can participate in blood donation, and each time they can donate 200-400 ml. The interval between two blood donations should be 6 months. Healthy people donate blood according to regulations, which will not have any impact on their health, and will not "hurt their vitality", but will be beneficial to health. First, the blood stored after blood donation will be replenished immediately, and the circulating blood volume will not decrease. Water and inorganic substances lost after blood donation were replenished within 1 ~ 2 hours, and platelets, white blood cells and red blood cells quickly recovered to their original levels. At any time, many blood cells are aging and dying, and a large number of new cells are produced to maintain the balance of human metabolism. After blood donation, the lost blood cells were quickly replenished because of the enhancement of hematopoietic function. Therefore, as long as it does not exceed the stored blood volume, it will not cause harm to the body, but also stimulate hematopoietic function and increase blood circulation, so choose B.