关于安全用电,下列说法不正确的是( )
A:使用测电笔辨别火线时,手要接触笔尾的金属电极
B:插座中的两个线头接触会出现短路现象
C:家庭电路中的空气开关跳闸后,直接合上空气开关就可以了
D:家庭电路中,控制各个灯的开关都要安装在火线上
A man says to his friend,"Guess how many coins(硬币) I have in my pocket(兜). "
The friend says. "If(如果) I guess right,will you give me one of them?"
The man says,"If you guess right,I'll give you both(两个都) of them. "
已知等差数列an和等比数列bn,它们的首项是一个相等的正数,且第3项也是相等的正数,则a2 与b2的大小关系为( )