The shoes are _____ than I expected.

A．far expensive

B．far too expensive

C．far much expensive

D．far more expensive

n元线性方程组Ax=b有唯一解的充要条件是( )

A．A为可逆的方阵

B．齐次线性方程组AX=0只有零解

C．A的行向量组线性无关

D．矩阵A的列向量线性无关，且向量b可由A的列向量组线性表示-