(D) Alfred Crosby is the author of The Columbian Exchange (referenced in Ecological Imperialism cited in the chapter).
The passage in Box 1 cites Alfred Crosby's Ecological Imperialism, and he is well known for coining the term "Columbian Exchange." The other options — Marco Polo, Columbus, and Vasco da Gama — were explorers, not authors of this work. For MCQs, always link the name to its specific work as mentioned in the textbook.