单选题 Not until ten o'clock ______ it was too late to return.
A. did we realize B. we did realize
C. realized we D. we realized

【正确答案】 A

【答案解析】[解析] not until...置于句首时，主句要用倒装语序。以否定词not/never引导的状语放在句首、以nor/neither及半否定词seldom/hardly/rarely/little等放在句首时，句子均须用半倒装语序。