选择与图片对应的句子( )
A:It's a classroom .
B:It's a school.
若两条抛物线的顶点相同,则称它们为“友好抛物线”,已知抛物线C1:y1=﹣x2+ax+b与抛物线C2:y2=2x2+4x+6为“友好抛物线”,抛物线C1与x轴交于点A、C,与y轴交于点B.