If A=(45)A = \begin{pmatrix} 4 & 5 \end{pmatrix}A=(45), what is ATA^TAT?
(45)\begin{pmatrix} 4 \\ 5 \end{pmatrix}(45)
(54)\begin{pmatrix} 5 \\ 4 \end{pmatrix}(54)
(45)\begin{pmatrix} 4 & 5 \end{pmatrix}(45)
(54)\begin{pmatrix} 5 & 4 \end{pmatrix}(54)