◎ 题干
Only when he returned from the exchange program ________ how much he enjoyed it.
[      ]
A.  he knew  
B.  he had known
C.  did he know  
D.  had he known
◎ 答案
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◎ 解析
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◎ 知识点
    根据n多题专家分析,试题“Only when he returned from the exchange program ________ how much he enjoyed it.[ ]A.he knewB.he had knownC.did he knowD.had he known…”主要考查了你对  【一般过去时】【部分倒装】  等知识点的理解和应用能力。关于这些知识点的“档案”,你可以点击相应的链接进行查看和学习。