Karl landsteiner placed animal blood in human blood and discovered that the blood clumped. which did his creativity lead to?
understanding the process of blood clotting
understanding the formation of blood cells
understanding the function of antibodies
understanding a, b, ab, and o blood groups

Karl Landsteiner's creativity led to D. understanding A, B, AB, and O blood groups. Based on him experimenting with animal and human blood, 3 different blood types were created according to their reactions with each other. Those three blood groups were A, B, and O, whereas the fourth group, AB, was named some time after the introduction of the first three. He discovered that when red blood cells of one group are added into another group, it results in clumping of red cells and their antigens and antibodies, which led him to naming these four types of blood.