Row echelon form

Choose the matrices that are in reduced row echelon form:

$A=\begin{pmatrix} 1 & 2 & 0 & 0 & 0\\ 0 & 4 & 5 & 0 & 0\\ 0 & 0 & 1 & 8 & 4\\ 0 & 0 & 0 & 1 & 0\\ \end{pmatrix}$ $B=\begin{pmatrix} 1 & 8 & 0 & 0\\ 0 & 2 & 0 & 0\\ 0 & 0 & 1 & 0\\ 0 & 0 & 0 & 1\\ \end{pmatrix}$ $C=\begin{pmatrix} 1 & 0 & 0\\ 0 & 0 & 1\\ 0 & 0 & 0\\ \end{pmatrix}$ $D=\begin{pmatrix} 1 & 0 & 0 & 0 & 8\\ 0 & 1 & 0 & 0 & 0\\ 0 & 0 & 1 & 0 & 0\\ 0 & 0 & 0 & 1 & 0\\ \end{pmatrix}$