Question

Not until I began to work ________ how much time I had wasted．

1. A.
   didn't I realize
2. B.
   did I realize
3. C.
   I didn't realize
4. D.
   I realized

Answer 1

B
not until 放在句首时，它连接的时间状语不倒装，主句应倒装，因此只有B是最佳答案。