药材断面有一条凸起的棕黄色环纹,在紫外光灯(254nm)下,断面显淡紫色荧光,而凸起的木质部显黄色荧光,该药材是()
A、黄连
B、狗脊
C、龙胆
D、延胡索
参考答案:B
Mr. Black _____ for Shanghai in a few days. Do you know when the earliest plane ____on Sunday?
A.leaves; takes off
B.is leaving; takes off
C.is leaving; is taking off
D.leaves; is taking off
套筒滚子链的链板一般制成“8”字形,其目的是()
A.使链板美观
B.使链板各截面强度接近相等,减轻重量
C.使链板减少摩擦
D.减少链条与链轮间的摩擦和磨损