What is the result of the matrix product (1001)(abcd)\begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix} \begin{pmatrix} a & b \\ c & d \end{pmatrix}(1001)(acbd)?
(1111)\begin{pmatrix} 1 & 1 \\ 1 & 1 \end{pmatrix}(1111)
(abcd)\begin{pmatrix} a & b \\ c & d \end{pmatrix}(acbd)
(0000)\begin{pmatrix} 0 & 0 \\ 0 & 0 \end{pmatrix}(0000)
(acbd)\begin{pmatrix} a & c \\ b & d \end{pmatrix}(abcd)