避雷线的接地引下线常用材料一般采用（）。
A．镀锌钢绞线
B．钢芯铝绞线
C．铜线
D．铝线
参考答案：A
过点A（4，2）向圆 x=4cosθy=4sinθ
I don't believe we've met before, ________ I must say you do look familiar. [ ]
A. therefore
B. although
C. since
D. unless
