a
$A=\left[\begin{array}{ccc}2 & -1 & -1 \\ 1 & 0 & -1 \\ 1 & -1 & 0\end{array}\right] \Rightarrow A^{2}=A \Rightarrow A^{n}=A$
Now, $B = A - I =\left[\begin{array}{lll}1 & -1 & -1 \\ 1 & -1 & -1 \\ 1 & -1 & -1\end{array}\right]$
$B ^{2}=- B$
$B ^{3}=- B ^{2}= B$
$B ^{5}= B$
$B ^{99}= B$
Also, $\omega^{31}=1$
So, $n =$ common of $\{1,3,5, \ldots, 99\}$ and
$\{3,6,9, \ldots, 99\}=17$