19. Compared to the author of Passage A, the author of Passage B provides more information about the:
A. reduction in the number of apple varieties in North America over the past four centuries.
B. methods Vavilov used to prove to other scientists that the apples growing in the Tian Shan are the ancestors of the modern apple.
C. number of apple varieties that are thriving in Kazakhstan today.
D. techniques used by researchers to determine the regions with the greatest genetic diversity in plants.