Which of the following matrices is a diagonal matrix?
(1201)\begin{pmatrix} 1 & 2 \\ 0 & 1 \end{pmatrix}(1021)
(1005)\begin{pmatrix} 1 & 0 \\ 0 & 5 \end{pmatrix}(1005)
(0110)\begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix}(0110)
(1111)\begin{pmatrix} 1 & 1 \\ 1 & 1 \end{pmatrix}(1111)