Not until the teacher explained the importance of getting up early we promise to e early.
A. should
B. would
C. did
D. could
网友回答
A. should
B. would
C. did
D. could
解析：考察倒装句。Not until放在句首时，后面的主句使用部分倒装的形式。后面主句的promise是谓语动词，所以使用助动词did.句意：直到老师届时了早起的重要性的时候，我们才允诺会早点来。