Given A=(2101)A = \begin{pmatrix} 2 & 1 \\ 0 & 1 \end{pmatrix}A=(2011), what is ATA^TAT?
(2011)\begin{pmatrix} 2 & 0 \\ 1 & 1 \end{pmatrix}(2101)
(1210)\begin{pmatrix} 1 & 2 \\ 1 & 0 \end{pmatrix}(1120)
(2101)\begin{pmatrix} 2 & 1 \\ 0 & 1 \end{pmatrix}(2011)
(1012)\begin{pmatrix} 1 & 0 \\ 1 & 2 \end{pmatrix}(1102)