The correct answer is d. Louis Pasteur and the name for his finding is the Gem Theory of disease - the theory that disease is caused by Gems - until then people didn't know this. He did this by working on a plague of silkworms.
He also proved that fermentation is caused by microorganisms.
It would be "d. Louis Pasteur"--a French chemist--who was the first person to determine that germs caused disease, since this was a major breakthrough in both medicine and science in general.
