Final answer:
The association of specific microorganisms with specific illnesses was made possible by the Germ Theory, which was substantiated by the work of notable scientists such as Louis Pasteur and Robert Koch following the invention of the microscope.
Step-by-step explanation:
The advancement that made the association of specific microorganisms with specific illnesses possible was B) Germ Theory. The invention of the microscope by Antonie van Leeuwenhoek allowed for the observation of bacteria and laid the groundwork for germs to be associated with disease. However, it was the germ theory of disease, further developed by scientists like Louis Pasteur and Robert Koch, that revolutionized the medical field by definitively linking specific pathogens to specific diseases. Pasteur's discovery that microorganisms cause fermentation and spoilage led to pasteurization and vaccines against diseases such as anthrax and rabies. Koch identified the specific microbes responsible for diseases such as anthrax, cholera, and tuberculosis. Their work substantiated the germ theory, which holds that many diseases are caused by microorganisms.