Why does the author mention "the enormous stretches of ocean that separate the Southern Hemisphere continents today" A. To emphasize the importance of the famous European voyages of discovery in the eighteenth and nineteenth centuries B. To suggest a reason why so many genera of flowering plants are found only in the Southern Hemisphere C. To question the accuracy of Sir Joseph Dalton Hooker's observations about the similarities between the flora of Australia and that of South America D. To explain why the similarities between flora pointed out by Sir Joseph Dalton Hooker seemed so remarkable