画轴测图时，应以管道（）为基础，弄清楚管线的空间走向，并确定同各轴的关系，然后绘制轴测图。
A、平面图
B、原理图
C、立面图
D、详图
参考答案：A, C
Mr. Blake ____ Shanghai in a few days. Do you know when the earliest plane ____ on Sunday?
A．is leaving, takes off
B．leaves, takes off
C．is leaving, is taking off
D．leaves, is taking off
南极地区有代表性的动物是______，北极地区有代表性的动物是______．
