Which of the following is considered a secondary source?
a. a news magazine article about migrant farm workers in california
b. a collection of interviews with migrant farm workers
c. a u. s. department of agriculture report on farm labor statistics
d. a letter written by a migrant farm worker to his family

A primary source was created at the time been studied or a short time after. Statistics , Letters and interviews are created/done at the time been studied.  So the magazine article would not be a primary source thus been secondary.

Urban growth invariably feeds increased commercialization and industrialization. it requires continually expanding land areas. when urbanization rates are high, and countries do not have the institutional and managerial capacities or economic wherewithal to manage such rapid growths, they exert intense pressure on the types and nature of the resulting settlements. they contribute to the development of overcrowded slums and shanty towns without adequate essential services and necessary infrastructure.-by asit k. biswas and cecilia tortajada