题文
.I had been puzzled over the problem for over an hour without any result, _____ all at once thesolution flashed across my mind.
| A．while | B．when | C．then | D．as |
推荐试卷
.I had been puzzled over the problem for over an hour without any result, _____ all at once thesolution flashed across my mind.
| A．while | B．when | C．then | D．as |
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