The correct answer is A. Antonie van Leeuwenhoek.
Antonie van Leeuwenhoek was a Dutch draper and microscope maker who is generally credited with being the first person to see bacteria. He made simple microscopes with a single lens that could magnify objects up to 270 times. In 1674, he wrote a letter to the Royal Society of London describing the “animalcules” he had seen in a drop of water. These were the first bacteria ever observed.
Louis Pasteur was a French chemist and microbiologist who is considered one of the founders of modern medicine. He is best known for his work on fermentation, pasteurization, and vaccines. He did not see bacteria through a microscope.
Robert Hooke was an English physicist, anatomist, and microscopist who is best known for his work on microscopy. He is credited with being the first person to observe cells. He did not see bacteria through a microscope.
Robert Virchow was a German physician and pathologist who is considered one of the founders of modern pathology. He is best known for his cell theory, which states that all living things are made up of cells. He did not see bacteria through a microscope.