What is the basic sumerian building material

The basic Sumerian building material that were used for the construction purpose were bricks made of mud. Mud was in abundance near the banks of the river Tigris and Euphrates. The need for making the bricks out of the mud from the river banks arose due to the shortage of building quality stones. They used these mud bricks to construct huge buildings. the mud was shaper in the form of bricks and then burnt in fire to harden them. Ziggurats or stair cases were built in every city out of mud bricks during the sumerian period.

Idont know which one is right   but i know that c is wrong and a might be wrong