20.对数函数y=logax(a>0y=\log _{a}x(a>0y=logax(a>0且a≠1)a\ne 1)a=1)与二次函数y=(a−1)x2−xy=(a-1)x^{2}-xy=(a−1)x2−x在同一坐标系内的图象不可能是((( )))