用配方法解方程：x2﹣4x+2=0，下列配方正确的是[ ]
A．（x﹣2）2=2
B．（x+2）2=2
C．（x﹣2）2=﹣2
D．（x﹣2）2=6
答案：A
All possible means ____, but nothing can prevent the buildings ____. [ ]
A. has tried; from being pulled down
B. have tried; from pulling down
C. has been tried; from pulling down
D. have been tried; from being pulled down
同一口井的无线ZIGBEE设备的网络号、信道号必须相同，否则无法通讯。（）
