Let $A=\left[\begin{array}{ccc}4& 6& -1\\ 3& 0& 2\\ 1& -2& 5\end{array}\right]$, $B=\left[\begin{array}{cc}2& 0\\ -1& 4\\ 1& 2\end{array}\right]$, and $C=[312]$. The expression which is not defined is:

Check the dimensions:$A$ is $3\times 3$, $B$ is $3\times 2$, $C$ is $1\times 3$.$B^{T}B$: $B^T$ is $2\times 3$ and $B$ is $3\times 2$. Multiplication is possible ($2\times 3$ by $3\times 2$ results in $2\times 2$). Defined.$CAB$: $C(1\times 3)\times A(3\times 3)⟹1\times 3$. Then $(1\times 3)\times B(3\times 2)⟹1\times 2$. Defined.$A+B^T$: $A$ is $3\times 3$ and $B^T$ is $2\times 3$. Addition is only defined for matrices of the same dimension. Not defined.$A^2+A$: $A$ is square ($3\times 3$), so $A^2$ is $3\times 3$. Addition with $A$ ($3\times 3$) is possible. Defined.