若9x2+kx+1恰好为某一个整式的完全平方，则常数k的值是______．
∵9x2+kx+1恰好为某一个整式的完全平方，
∴k=±6．
故答案为：±6．
— Ann has made great progress recently.
— _____ and _____. [ ]
A. So has she, so have you
B. So has she, so you have
C. So she has, so you have
D. So she has, so have you
在正常情况下，阀型避雷器中（）。
A、无电流流过
B、流过工作电流
C、流过工频续流
D、流过冲击续流
