Humans have a type of memory called immune memory. There are very few self-sacrifice cells in human blood. They live for a short time, and their main function is to destroy as many enemies as possible. Toxic substances respond quickly, generate antibodies, stick harmful substances to prevent them from entering other organs, and the task of destroying enemies lies on the head of phagocytes in the blood. These cells can effortlessly distinguish foreign cells To be able to remember them and retain their memories. Once a person has measles or scarlet fever, they will get lifelong immunity. What is the right thing to understand? ['The main function of phagocytes in human blood is to remember foreign cells that invade the body.', 'Lymphocytes can stick to the toxic substances that invade the blood and prevent them from entering other organs.', 'Phagocytes and lymphocytes in human blood are sacrificing cells.', 'Humans have immune memory, as long as they get measles and scarlet fever, they will get lifelong immunity.']