A:may take
B:may have been taken away
C:must have taken away
D:needn’t have been taken away
二次函数y=ax2+bx+c的图象如图所示,那么一次函数y=ax+b的图象大致是( )
安装家庭电路时,从进户线到用电器之间有闸刀开关、电能表、熔断器,它们正确的排列顺序应是( )
①f(a×b)=f(a)+f(b);②f(2)=1; ③当x>0时,f(x)>0.