The correct answer is B. The interaction of people spread the plague.
Step-by-step explanation
During the 14th century, the Black Death pandemic occurred between the continents of Asia and Europe. According to the statements of the question, it can be interpreted that the Black Death is related to merchants and the movements of people between the continents of Europe and Asia. Also, the ports had a great incidence in the spread since the fleas of the black rats that inhabited the ships transmitted the virus to the humans. So the correct answer is B. The interaction of people spread the plague.