a
Given that
$A = \left[ {\begin{array}{*{20}{c}}
0&{ - 1}\\
1&0
\end{array}} \right]$
${A^2} = \left[ {\begin{array}{*{20}{c}}
{ - 1}&0\\
0&{ - 1}
\end{array}} \right] \Rightarrow {A^2} = - I$
${A^3} = \left[ {\begin{array}{*{20}{c}}
0&1\\
{ - 1}&0
\end{array}} \right]$
${A^4} = \left[ {\begin{array}{*{20}{c}}
1&0\\
0&1
\end{array}} \right] = I$
${A^2} + I = {A^3} - A$
$ - I + I = {A^3} - A$
${A^3} \ne A$