问题补充：
He used to his teaching when he was young.
A. devote to
B. be devoted to
C. devoting to
D. being devoted to
答案：
A. devote to
(答案→)B. be devoted to
C. devoting to
D. being devoted to
解析：used to 接动词原形表示”过去常常”；”致力于”应该是devote one-selt to 或be devoted to…，所以答案为B。
