In an effort to protect themselves, all of the kingdoms of sumer built outside their cities.
a. large moats
b. deep trenches
c. massive walls
d. watch towers

1.       In an effort to protect themselves, all the kingdom of summer built massive walls outside their cities. By this, they will be able to protect themselves from their opponent’s surprise attacks. Their walls were made up of stones and mud bricks, and woods. These walls measured 5.9 miles in length and 39 feet in height. These walls also served as their defense to win their battle. By building walls their opponents cannot easily enter their cities. However, some of their enemies dig up tunnels under their walls to be able to enter. Their defenders used smokes into the tunnels to protect their city from them

Ibelieve that the answer is (a).