Задание 39 ЕГЭ по английскому языку

Modern medicine is developing very fast. New important discoveries are made by scientists every day. Still, you should not think that in ancient times medicine was primitive. In the Roman Empire doctors made very important discoveries. Without them modern medicine would have been impossible. Roman doctors were mainly Greek slaves. At first they were poor and had a very low status. Later Roman doctors began to write books about illnesses and their treatment. In the first century BC a Roman doctor suggested that tiny animals like rats caused disease. Unfortunately with no modern equipment there was no way of testing his theory. The Romans were also skilled engineers, and they created a system of public health. They also knew that dirt could be a reason for disease. That is why they paid special attention to keeping their towns clean.