The earth ________ to be flat．
A.was used to be thoughtB.used to be thoughtC.was used to thinkD.used to think在线课程B
解析：
be used to doing指“习惯于”；be used to do指“被用来做”；used to do指“曾经，(以前)常常”。而本句后的to be flat作think的宾语补足语。