Problem: Humans have been making yogurt for thousands of years and beer for several hundred years
Which of the following is true:
a Humans could make these products without knowing the existence of microbes.
b. Unlike today, humans back then could make these products without the assistance of microbes
c. At least some humans must have known about the existence of microbes; in order to make the products.
d. Scientists and historians are still puzzled how humans could make these products.