Which of the following pieces of data would be most to a researcher who would like to study mortality rates in british cities during the industrial revolution? a. a chart showing an increasing gap between the rich and poor starting in the industrial revolution b. a list of the average salaries paid to workers at different factories in a large industrial city c. a physical map showing the spread of railroad tracks across great britain during the 19th century d. a set of newspaper articles listing the age of each deceased person in various british cities over several years