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A.加热冷凝法 B.石油醚或乙醚回流提取法 C.碱水加热提取加酸沉淀法 D.水蒸气蒸馏法 E.硅胶层析法 结构相近的香豆素分离需用

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The Indians had invented the hammock long before the Europeans came to South America.

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Passage One Questions 26 to 28 are based on the passage you have just heard.

A. Gourmet coffee is less expensive.
B. Regular brands of coffee have too much caffeine.
C. Gourmet coffee tastes better.
D. Gourmet coffee is grown in the United States.

A.二蒽酮苷类 B.大黄素型 C.苯醌类 D.茜草素型 E.菲醌类 蒽醌的羟基分布在两侧苯环上称为

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