The correct answer is A. A. Fleming.
Penicillin was discovered by Alexander Fleming in 1928. He was a Scottish bacteriologist who was working at St Mary’s Hospital in London. He noticed that a mold had grown on one of his petri dishes and that the bacteria around the mold had died. He isolated the mold and named it Penicillium notatum. He then showed that penicillin could kill a wide range of bacteria, including those that cause pneumonia, meningitis, and scarlet fever.
Paul Ehrlich was a German physician and scientist who is considered one of the founders of modern pharmacology. He is best known for his work on the development of salvarsan, the first effective treatment for syphilis. He also developed a number of other drugs, including arsphenamine, which was used to treat malaria.
Gregory Mendel was an Austrian monk and scientist who is considered the father of genetics. He is best known for his work on pea plants, in which he showed that traits are passed down from parents to offspring in a predictable way. His work laid the foundation for the modern science of genetics.
Dr Jonas E. Salk was an American physician and virologist who is best known for developing the polio vaccine. He was also a co-founder of the Salk Institute for Biological Studies.