sentence: Some scientists believe that the plague spread faster than the rats.
sentences_before: Those rats lived in the European cities of the day, and died of the plague themselves.
sentences_after: If this is true, the rats cannot be the main carrier. More research is needed to find out if this is true. People believe this disease was the Black Death. It killed nearly a third of the population of Europe, in many epidemics in the Middle Ages.
concept_name: scientist
headings: Rat Carriers of disease
categories: Basic English 850 words Old World rats and mice Omnivores