One of the occasional problems faced by people settling along the tigris and euphrates rivers was the fact that: o both rivers had several high waterfalls. o both rivers were home to large populations of crocodiles. o the course of each river changed over time. the course of each river could dry up during hot summers.

The course of each river changed over time.

Explanation:

One of the major problems associated with the river water system sis that these have changing courses over some time as the rivers become dry or are captured by another river from the source or other geologic formations. The population of people living in the Euphrates and Tigris rivers perished due to the availability of fertile lands and water sources. Due to this, the alluvial fan has also got shifted. The turning away of river courses these two rivers that fed the massive dams of keban and Ataturk dam which were massive irrigation projects reduced the water flow to the major cities, thus leading disputes of war and the Perishing of the civilization.

H=   2(area/a+b)h= 2(144/a+b)h= 2(144/18+18)h= 2(144/36)h= 2(4)h=8

980 is the correct answer