Concept:Settlement types are ranked by size, from a single city to a vast urban region.Explanation:A city is a single urban area.An agglomeration is a city and its surrounding built-up suburbs.A conurbation forms when several towns and cities merge into one continuous urban area.A megalopolis is an even larger urban region created when several conurbations or major cities grow together.Therefore, megalopolis is the largest settlement type among the options.Answer:C. Megalopolis