The correct answer is C. Karl Landsteiner.
Karl Landsteiner was an Austrian physician and immunologist who is best known for his discovery of the ABO blood group system in 1900. He also discovered the Rh factor in 1940. Landsteiner’s work on blood groups was a major breakthrough in medicine, and it has saved countless lives.
Krebs is a German biochemist who is best known for his discovery of the Krebs cycle, also known as the citric acid cycle. The Krebs cycle is a metabolic pathway that is essential for the production of energy in cells.
Pavlov was a Russian physiologist who is best known for his work on classical conditioning. Classical conditioning is a type of learning in which an organism learns to associate a stimulus with a response. Pavlov’s work on classical conditioning has had a major impact on psychology and neuroscience.
Darwin was an English naturalist who is best known for his theory of evolution. Darwin’s theory of evolution is the idea that all species of life have evolved over time from common ancestors. Darwin’s theory of evolution is one of the most important and influential theories in science.