Answer: Alexander Fleming discovered penicillin, Wilhelm Roentgen discovered X-rays and Robert Koch founded the science of bacteriology.
Explanation: Alexander Fleming was a Scottish bacteriologist who lived during the late nineteenth century and the first half of the twentieth century. He discovered penicillin, which has been used to treat serious illnesses, in 1928 and received the Nobel Prize in 1945 for it. Wilhelm Roentgen was a German physicist who discovered X-rays, a form of electromagnetic radiation, in 1895. Finally, Robert Koch was a German physician. Furthermore, he is considered the father of bacteriology, the science that studies bacteria. Moreover, he was awarded the Nobel Prize in Physiology or Medicine in 1905.