Answer:
D. Ethos, because the author uses an expert source to make his argument more credible
Step-by-step explanation:
Ethos is a mode of persuasion that mentions a source or figure that shows credibility, expertise, prestige or character in order to convince people that the information is reliable, valid, and is worth listening. In the excerpt, Norman Borlaug is that expert source. Since he is a Nobel Prize-winning agronomist, and was also supported by the Rockefeller Foundation (a very prestigious company), then, his "miracle wheat" program should also be seen as reliable, and one of the best option to enhance agriculture.