A:2
B:4
C:6
D:8
— did you stay in the library?
— I stayed there for over two hours.
如图示意黄河干流沿河堤剖面及各河段干流长度,读图完成以下问题。
抛物线y=ax2+bx+3经过点A(1,0)和点B(5,0).