钩藤的有效成分是
A．挥发油B．香豆精C．生物碱D．皂苷E．黄酮
参考答案：C
解析：钩藤主要含生物碱类成分。故答案选C。
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It is easy enough to download and copy, but you should at least write ________ by yourself.
A．anything
B．everything
C．something
D．nothing
下列水电站或水利枢纽位于黄河干流的是[ ]
A．飞来峡水电站
B．三门峡水电站
C．三峡水利枢纽
D．丹江口水电站
