The Following Questions Refer to the Excerpt Below

The following questions refer to the excerpt below.
"[The land in the New World] is a marvel;the mountains and hills,and plains,and fields,and land,so beautiful and rich for planting and sowing,for breeding of cattle of all sorts,for building of towns and villages…there are many spiceries,and great mines of gold and other metals. The people of this island,and of all the others I have found and seen,or not seen,all go naked,men and women,just as their mothers bring them forth….as soon as I arrived in the Indies,in the first island that I found,I took some of them by force to the intent they should learn [our speech] and give me information of what there was in those parts."
Letter from Christopher Columbus to Luis de Santángel,1493
-Which of the following had the most significant impact on developing the economy (as described in the passage) ,which would evolve between 1491 and 1607?

A) The growth of racially mixed populations in the Americas
B) The development of sophisticated transportation networks
C) Increasingly complex cultural exchanges between Europeans and natives
D) The introduction of slave labor and the encomienda system