How does Boccaccio let you know that he recognized that the plaque spread widely from one location to another?

I found the answer choices and provided them below:

How does Boccaccio let you know that he recognized that the plague spread widely from one location to another?

a) He states that it was caused by rats.

b) He states that it caused reckless behavior.

c) He states that it spread from the Middle East.

d) He states that people did not avoid the sick

The best answer choice for this question would be A.

He gives a speech about the plaque and ways he is going to stop it