摘要： 若 (b-1)2 + a2 = 0, 则下列方程中是一元二次方程的是 ( ) A. ax2 + 5x -b = 0 B. (b-1)x2 + x -5 =0 C. (a-1) x2 + (b-1)x-7 = 0 D. (b-1) x2 + ax -1 = 0

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