—______?  

—Tom.      [ ]

A. What color is it          

B. What's his name      

C. How is he                

D. Are you Mark

设A为n阶矩阵，A经过若干次初等行变换后的矩阵记成B，则

A．Ax=b与Bx=b同解．

B．Ax=0与Bx=0不同解．

C．|A|=|B|．

D．A，B的列向量组的极大线性无关组的向量个数相同．