A. Fleming: Alexander Fleming is credited with the discovery of penicillin in 1928 when he observed that the mold Penicillium notatum produced a substance that killed or inhibited the growth of certain bacteria. B. Ehrlich: Paul Ehrlich is known for his work in immunology and for developing the concept of a "magic bullet" in chemotherapy, as well as discovering Salvarsan for treating syphilis, but he was not involved in the discovery of penicillin. C. Pasteur: Louis Pasteur made groundbreaking contributions to microbiology and germ theory, including pasteurization and vaccines for rabies and anthrax. D. Lister: Joseph Lister pioneered antiseptic surgery and promoted the use of carbolic acid to prevent infections during surgical procedures, but he did not discover penicillin.