What led to the demise of the classic Mayans? List the four theories.
PLZ HELP

They were wiped out by another empire.

They all died of starvation.

There was a terrible illness.

They were killed in a natural occurrence. (earthquake, tornado, etc.)

Explanation:

these are the theories I can think of, but it says THE four theories. Therefore, it may be in any reading or notes you were given

The big problem with the Mississipi River being a political boundary is that rivers move along the time (they change their course).

Explanation:

Rivers change their course because on the faster side of the river less sediment is deposited. Where the water is flowing faster the land erodes and small curves are formed. At the slower part of the river more sediment from erosion is deposited. This way, a river changes its course.