有黄酮基本母核，且3位有含氧基团取代的化合物是（）
A. 异黄酮
B. 黄酮醇
C. 二氢黄酮醇
D. 黄烷醇
E. 二氢黄酮
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燃煤长管爆炸性实验，返回火焰长度大于400mm，为（）煤种。
神华质量标准化规定综采支架要垂直顶底板，歪斜小于±7°。
A. 正确
B. 错误
Which of the following statements are true regarding bridges and switches?（）
A. Switches are primarily software based while bridges are hardware based.
Both bridges and switches forward Layer 2 broadcasts.
C. Bridges are frequently faster than switches.
D. Switches have a higher number of ports than most bridges.
E. Bridges define broadcast domains while switches define collision domains.
F. Both bridges and switches make forwarding decisions based on Layer 2 addresses.
根据干扰波和有效波之间的差别,采用组合法可以消除干扰波.
A. 正确
B. 错误
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