Which of these matrices is in Row Echelon Form (REF)?
(0110)\begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix}(0110)
(1203)\begin{pmatrix} 1 & 2 \\ 0 & 3 \end{pmatrix}(1023)
(0100)\begin{pmatrix} 0 & 1 \\ 0 & 0 \end{pmatrix}(0010)
All of the above