Much of south america falls within the tropical humid and tropical wet and dry climate zones, as indicated by the two shades of purple on the above map. which of the following statements best explains why much of the western coast is colored dark brown? a. the dark brown represents the marine west coast climate zone. b. the dark brown represents the arid climate zone: the western portion of the continent is a desert. c. the dark brown represents the highland climate zone, and the andes mountains are located along the western portion of the continent. d. the dark brown represents the highland climate zone, and the sierra madres are located along the western portion of the continent.