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What kind os source would a historian use to get a firsthand account of a past event

Before 2010, haitian refugees were returned to their country without asylum hearings because

The largest city in brazil, sao paulo, has a population of about 11 million. based on the rank-size rule, what is the population of the second-largest city, rio de janeiro, most likely to be? a. 8 – 10 million b. 5 – 6 million c. about 3 million d. about 1 million