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# If $\overrightarrow {a}$ and $\overrightarrow{b}$ are unit vectors, then the vector $(\overrightarrow a+\overrightarrow b) \times (\overrightarrow{a} \times \overrightarrow{b})$ is parallel to the vector:

$\begin {array} {1 1} (a)\overrightarrow {a}-\overrightarrow {b} & \quad (b)\;\overrightarrow {a}+\overrightarrow {b} \\ (c)\;2\overrightarrow {a}-\overrightarrow {b} & \quad (d)\;2\overrightarrow {a}+\overrightarrow {b} \end {array}$