If $\vec{a} \cdot (\hat{i} + \hat{j}) = \vec{a} \cdot (\hat{i} + \hat{j} + \hat{k}) = 1$, then $\vec{a} = $

Question

$\hat{i} + \hat{j}$

$\hat{i} - \hat{k}$

$\hat{i}$

$\hat{i} + \hat{j} - \hat{k}$

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