What does the author mean when he says “of these three trembling cities the greatest is the last”?

Laura is writing a report about the natural resources of mississippi. she will collect information about the natural resources from many different sources. one will be a multimedia encyclopedia. when she searches for information in a multimedia encyclopedia, she finds four results. three of the results will laura, but one will not her. which of these articles will not laura write her report? a) "the oil of mississippi" b) "the timber of mississippi" c) "the politics of mississippi" d) "the natural gas of mississippi"