Let the vectors $\vec{a}$and $\vec{b}$be such that $\left|\vec{a}\right|=3$and $\left|\vec{b}\right|=\frac{\sqrt{2}}{3}$, then $\vec{a}\times \vec{b}$is a unit vector, if the angle between $\vec{a}$and $\vec{b}$
(A) $\pi /6$ (B) $\pi /4$ (C) $\pi /3$ (D) $\pi /2$

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