◎ 题干
The problem is very hard. He thought of it for a long time._______ he solved it.   
[     ]
A. In the end    
B. At the end of    
C. by the end of    
D. In the end of
◎ 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“The problem is very hard. He thought of it for a long time._______ he solved it.[ ]A. In the endB. At the end ofC.by the end ofD.In the end of…”主要考查了你对  【介词短语】  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。