求下面矩阵的LU分解\begin{bmatrix} 4\ \ 1\ \ 2\ \ 1\\ 1\ \ 3\ \ 2\ \ 4\\ 2\ \ 2\ \ 1\ \ 2\\ 3\ \ 1\ \ 2\ \ 1\\ \end{bmatrix}

A． timely feedback -- explain why an almost correct answer is wrong
B．
C．
D．
E．