Which of these matrices is a row vector?
(123)\begin{pmatrix} 1 \\ 2 \\ 3 \end{pmatrix}123
(12)\begin{pmatrix} 1 & 2 \end{pmatrix}(12)
(1001)\begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix}(1001)
(10)\begin{pmatrix} 1 \\ 0 \end{pmatrix}(10)