Almost seven tons of amber the Amber Room.
A. was used to make
B. was used to making
C. were used to make
D. were used to making
网友回答
A. was used to make
B. was used to making
(答案→)C. were used to make
D. were used to making
解析：考查主谓一致。seven tons of amber七吨的琥珀，谓语动词用复数，be used to do sth.被用来做某事，故选C。