The answer is B: mold.
The history of the first antibiotic —penicillin— revolves around observations and discoveries that date to ancient societies and that evolved during the centuries, although, in hard scientific terms, it was Alexander Fleming, a Scottish microbiologist, who first suggested that a form of Penicillium mold secreted an antibacterial matter. Fleming then went on to synthesize the active substance behind this antibacterial and he called it penicillin in 1928.