When was penicillin first tested and on what?

• A. 1942, rabbits
• B. 1940, mice
• C. 1950, dogs
• D. 1939, humans

Answer: (B)

The key idea is how penicillin was first demonstrated to work in a living organism before trying it in people. In 1940, researchers tested penicillin on mice that had bacterial infections and found that the drug could save lives and limit the infection. This animal proof-of-concept was crucial; it showed penicillin had real, controllable effects in an organism, paving the way for human testing that followed in the early 1940s. So the best choice is the one that states 1940 and mice.

The other options don’t fit the established sequence or facts. Human testing did not begin in 1939, and it wasn’t the first demonstration. The earliest animal test wasn’t in rabbits, and the date isn’t 1942 or 1950, which come after the initial mouse study and after the key early work that established penicillin’s potential.