\[V=\text {span}\left (\begin{bmatrix}1\\2\\-1\\1\end{bmatrix},\begin{bmatrix}0\\2\\1\\-1\end{bmatrix}, \begin{bmatrix}2\\2\\-3\\3\end{bmatrix}, \begin{bmatrix}-1\\-2\\1\\-1\end{bmatrix}\right ) \]
\[\text {dim}(V)=\answer {2}\]