What is the dimension of the subspace of M2,2M_{2,2}M2,2 spanned by the matrices (1000),(0100),(1100)\begin{pmatrix} 1 & 0 \\ 0 & 0 \end{pmatrix}, \begin{pmatrix} 0 & 1 \\ 0 & 0 \end{pmatrix}, \begin{pmatrix} 1 & 1 \\ 0 & 0 \end{pmatrix}(1000),(0010),(1010)?
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