In the past,ice food.
A. used to keep
B. used to be used for keeping
C. was used to keeping
D. used to be used to keeping
网友回答
A. used to keep
(答案→)B. used to be used for keeping
C. was used to keeping
D. used to be used to keeping
解析：考查情态动词的被动语态。句中used to be used for keeping中的used to是情态动词，意思是“过去常常”，而be used for 是动词use 的被动形式；这个句子还可以表达成：was used to keep 或used to be used to keep。