A map of North America with international borders, state borders, and province borders is shown. The map legend displays four types of borders. State and province borders are shown as a gray line and international borders are shown with a thick dark line. State river boundaries are shown with a thin blue line and international river boundaries are shown with a thick blue line.
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Which of the following statements is true about the map above?
a The border between Texas and New Mexico is a thin line, indicating a national border.
b The border between Alaska and British Columbia is a thick line, indicating a national border.
c The border between Haiti and the Dominican Republic is a thin line, indicating a state border.
d The border between North Dakota and South Dakota is a thick line, indicating a state border.