The earth ________ to be flat．

A.was used to be thought

B.used to be thought

C.was used to think

D.used to think

答案及解析： 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。