In Problems 1-5, perform the indicated matrix operations, if possible, where \[\begin{array}{ll}{[\mathrm{A}]=\left[\begin{array}{rr}1 & 0 \\2 & -1\end{array}ight]} & {[\mathrm{B}]=\left[\begin{array}{rrr}2 & -1 & 0 \\1 & 0 & 1\end{array}ight]} \\
{[\mathrm{C}]=\left[\begin{array}{rr} 2 & 0 \\1 & 2 \\-1 & 1\end{array}ight]} & {[\mathrm{D}]=\left[\begin{array}{rrr}0 & 1 & 0 \\-1 & 0 & 0 \\0 & 1 & -1\end{array}ight]}\end{array}\]

\([\mathrm{A}][\mathrm{B}][\mathrm{C}]\)