D) Most water and mud behave the same throughout time.
Answer:
The transport or circulatory system.
Disease: atherosclerosis.
How do I know: presence of a blood vessel (as indicated by the red blood cells within it) and the deposit of fat and/or cholesterol within the walls of the blood vessel.
Answer:
A market for cats would have had a positive externality.
Because the cats would kill the rats on sight since that is their natural behavior.
However, it is interesting to mention, that the cat's killing has been more of a "mythic" aspect of this story, since it fails to take into account that since the black death was caused by the<em> yersinia pestis</em> bacteria, cats could have been also infected, and since their interactions with humans are greater than rats or fleas, the real outcome could have been totally unexpected.
Well, I believe it to be true. As dirt roads, when they are wet tend to be harder to traverse. It largely depends on the context of the question, however
