1. by + 过去时间状语用过去完成时。
By last year I had learned 2000 English words.
2. 在no sooner … than, hardly … when, scarcely … when, barely … when等句型中,主句中的谓语用过去完成时,从句中的谓语用过去时。
No sooner had we got all the crops in than it began to rain.
She had hardly finished his speech when the audience started cheering.
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