How were the earliest Sumerian temples constructed?

How were the earliest Sumerian temples constructed?
 
  A) The earliest temples were constructed of mud brick called adobe and placed in the center of the city-state for all to see and attend to worship.
  B) The earliest temples were constructed of the only available substance (mud brick-adobe) and constructed atop man-made stepped mountains called ziggurats.
  C) Ziggurats were the earliest temples and they were constructed of stone and wood at the center of the city-state.
  D) The earliest temples were mountain temples that were built of brick at the highest point adjacent to the city-state.
  E) The ziggurats were the earliest temples constructed of mud brick and were constructed far from the city-state for worshippers to take a pilgrimage to interact with their deities.