The number of births and deaths among American Indians did not change dramatically during the 1970s. How would you explain the rise in their population during this same time period? a There was finally a category of Native Americans to check on the U.S. Census forms. b There was a high immigration rate from South and Central America. c More people began to think of themselves as American Indians and reported themselves to the U.S. Census as that. d None of the answers is correct.