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【单选题】
Claisen 缩合是用强碱催化的反应,也可用以增长碳链,从反应活性中心看,它们是:A.
一个羧酸酯出羰基，一个醛出 α-C
B.
一个羧酸酯出羰基，一个酮出 α-C
C.
两个羧酸酯，一个出羰基，一个出α-C
D.
两个醛或酮，一个出羰基，一个出 α-C
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举一反三
【单选题】She thought of her warm days with Tom and couldn't help crying.
A.
Thinking of her warm days with Tom, she couldn’t help crying.
B.
Thought of her warm days with Tom, she couldn’t help crying.
C.
To think of her warm days with Tom, she couldn’t help crying.
D.
Think of her warm days with Tom, she couldn’t help crying.
【简答题】怎样理解大力推进生态文明建设的重要意义?
【简答题】怎样理解大力推进生态文明建设的重要意义?
【简答题】Granny looked for her book，but she couldn’t find it_____.
【单选题】hard she tried, she couldn't control her feelings when she was told her baby had been found．
A.
As
B.
While
C.
However
D.
Although
【单选题】—Why isn’t Susan at the dance? —She couldn’t come because she hurt her foot. — !
A.
Don’t worry about her y
B.
Never mind
C.
That’s a shame
D.
Bad luck
【简答题】 用弹簧秤吊着一个铁球,浸没在水中而没有沉入容器底部,那么铁球受到的浮力的施力物体是 。
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