Final answer:
Walter Fiers did not discover penicillin, but made contributions to molecular biology and early genetic experiments.
Step-by-step explanation:
Fleming and his colleagues were credited with discovering and identifying penicillin, but its isolation and mass production were accomplished by a team of researchers at Oxford University under the direction of Howard Florey and Ernst Chain. They purified penicillin and showed its effectiveness as an antimicrobial agent in animal and human trials in the early 1940s. Ultimately, Fleming, Florey, and Chain were awarded the Nobel Prize in Physiology and Medicine in 1945.
On the other hand, Walter Fiers did not discover penicillin. He made significant contributions to the field of molecular biology and was involved in early genetic experiments, particularly in relation to the double-helix structure of DNA. However, option (d) is the correct answer for Walter Fiers.