Which of these matrices is not invertible?
(1101)\begin{pmatrix} 1 & 1 \\ 0 & 1 \end{pmatrix}(1011)
(1224)\begin{pmatrix} 1 & 2 \\ 2 & 4 \end{pmatrix}(1224)
(1001)\begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix}(1001)
(2112)\begin{pmatrix} 2 & 1 \\ 1 & 2 \end{pmatrix}(2112)