—_______ do you go to school?
—By school bus.
A:How
B:What time
C:Why
D:Which
当灾害发生时,图中行为正确的是( )
试证明关于x的方程(a2﹣8a+20)x2+2ax+1=0无论a取何值,该方程都是一元二次方程.