— Is your mother still a teacher?
— .
A. Yes, she was
B. She didn’t use to
C. No, but she used to
D. No, but she used to be
网友回答
A. Yes, she was
B. She didn’t use to
C. No, but she used to
(答案→)D. No, but she used to be
解析：选D。used to be表示“曾经是……”，与现在有对比之意。to后的be要保留。