蚯蚓头
参考答案：
指药材的根头部由叶柄脱落后留下的明显密集的横向环纹，因似虹蝴的头颈部而习称虹划头，如防风等。
文员作介绍，应先介绍地位高的人，再介绍地位低的人。
If of the air in a tank is removed with each stroke of a vacuum pump, what fraction of the original amount of air has been removed after 4 strokes ？（）
A.A
B.B
C.C
D.D
E.E
of the air in a tank is removed with each stroke of a vacuum pump, what fraction of the original amount of air has been removed after 4 strokes ？（）