I have to answer the following:

Let W be the subspace of $\displaystyle M_{2x2}(\mathbb{R})$ consisting of the set$\displaystyle \{$ $\displaystyle \left( \begin{array}{cc}

S=

0 & -1 \\

-1 & 1 \\

\end{array} \right) ,\left( \begin{array}{cc}

1 & 2\\

2 & 3\\

\end{array}\right) ,\left( \begin{array}{cc}

2 & 1\\

1 & 9\\

\end{array}\right) ,\left( \begin{array}{cc}

1 & -2\\

-2 & 4\\

\end{array}\right) ,\left( \begin{array}{cc}

-1 & 2\\

2 & -1\\

\end{array}\right)

$ $\displaystyle \}$generates W.

Find a subset of S that is a basis for W.

I am a little lost, can someone help me with this one, or at least a hint on where to go? Thanks