Why does the author mentions that "fossil angiosperm leaves, sterns, and pollen that were once in eastern South America and western Africa?" A. To provide support for the claim that angiosperms first appeared in the tropics B. To explain how scientists have determined the geographical location of supercontinents during Earth's early history C. To provide evidence that angiosperms evolved in similar ways in different parts of the world D. To challenge the idea that angiosperms spread toward the poles during the Cretaceous