Answer: B. if the foreigners had the power to cause the disease, so many of them wouldn't also have died.
Step-by-step explanation:
It has been estimated that diseases brought by the Europeans to the Americas led to the loss of 90% of Native Americans as they had no prior immunity to counteract the new diseases.
Europeans also died from those same diseases however as shown above with the death of 80% of them in this instance. De Vaca's host was able to stave off revenge killing on the Europeans by showing the Natives that Europeans were equally affected and so did not spread the disease on purpose.