A formal definition consists of three elements: term, class and differentia. Analyse the following definitions, and decide what element the underlined part is in each definition. Coronavirus, of the family Coronaviridae, is an animal virus associated with the common cold and other more serious conditions, such as pneumonia and severe acute respiratory syndrome (SARS). Due to mutation, some forms of Coronavirus are extremely contagious and potentially fatal. Individuals who experience persistent symptoms that increase in severity need to seek medical attention to prevent further illness and potential complications. The underlined part is (a) ______________