问题补充：
we had read your letter the true state of affairs.
A. It was until; that we understood
B. It was not until; we understood
C. Until; did not we understood
D. Not until; did we understood
答案：
A. It was until; that we understood
B. It was not until; we understood
C. Until; did not we understood
(答案→)D. Not until; did we understood
解析：句意：直到我们读了你的信，我们才理解事情的真实的状况。这里使用倒装句，not until放在句首，后面的主句要部分倒装，助动词did放在主语前面，注意不要和强调句It was not until…that…，混淆， 选D。
