For which of the following is Thucydides known?
Odeveloping an effective sewer system in ancient Greece, helping to reduce levels of disease in cities
Oobserving microbes, using a microscope, for the first time, even distinguishing between bacteria and fungi
Oproposing that disease was caused by microorganisms
Orealizing that people who had been infected by the Athenian plague had immunity to reinfection