Which of the following matrices is a row vector?
(12)\begin{pmatrix} 1 & 2 \end{pmatrix}(12)
(12)\begin{pmatrix} 1 \\ 2 \end{pmatrix}(12)
(1)\begin{pmatrix} 1 \end{pmatrix}(1)
(1234)\begin{pmatrix} 1 & 2 \\ 3 & 4 \end{pmatrix}(1324)