苏木的红色成分是
A．巴西苏木素B．巴西苏木色素C．色原烷类D．黄酮类E．挥发油
参考答案：B
_________ across the railway, a train hit it.
A．While walking
B．Walking slowly
C．As the little pig walking
D．While the little pig was walking
两个或多个群落之间的过渡区域称为（）.
