we had read your letter the true state of affairs.
A. It was until… that we understood
B. It was not until…that we understood
C. Until …did not we understand
D. Not until… we understood`
网友回答
A. It was until… that we understood
(答案→)B. It was not until…that we understood
C. Until …did not we understand
D. Not until… we understood`
解析：
这题考查强调句的用法：It’s not until…that…“直到…才”，句意是：直到我们读了你的信，我们才知道事情的真实情况。如果用not until在句首，从句需要倒装，所以D是错的。选B。