According to Guns, Germs, and Steel, the failure of North American Indians to domesticate the wild apple can be attributed principally to:
a) The Indian: the hunting and gathering lifestyle and cultural traits of the Indians made them little interested in domesticating plants.
b) The apple: North American apple species were less suitable to domestication than Eurasian apples.
c) Neither apple nor Indian: the problem has more to do with the total mix of plant and animal species available to North American Indians.
d) The European: the displacement of Indian populations by European colonists took away Indian access to wild apple regions.
Of these options, the best choice is Option C. In fact, Diamond says almost this exact thing on the last page of Chapter 8. This is page 156 in the paperback edition of the book. There, Diamond first says
…the reason for the failure of Native Americans to domesticate … apples … lay neither with the people nor with the apples.
Instead, Diamond says on that same page, the fault
…lay with the entire suite of wild plant and animal species available to Native Americans.
Thus, we can clearly see that C is the best choice.
D is clearly not correct. Diamond is talking about what happened before the Europeans came to the Americas. Thus, what the Europeans did in the Americas is not relevant to this question. B is not correct either. Diamond tells us that the apples were not really seriously different. He also mentions that many apples we eat today are descended from American apples, not European ones.
Most importantly, A is not correct. The argument made in A goes against Diamond’s entire argument in this book. The whole book is aimed at arguing that the people of the Americas and other places that got conquered were not at fault.
Instead, C is the best choice. There were simply not enough suitable plants and animals to allow for intensive agriculture in the Eastern US until very shortly before European contact. Therefore, C is the right answer.