If $(\vec{a}\times \vec{b})\times \vec{c}=\vec{a}\times (\vec{b}\times \vec{c})$, where $\vec{a},\vec{b}$ and $\vec{c}$ are any three vectors such that $\vec{a}\cdot \vec{b}\ne 0$ and $\vec{b}\cdot \vec{c}\ne 0$, then $\vec{a}$ and $\vec{c}$ are:

1. A
   inclined at an angle of $\pi /3$ between them
2. B
   inclined at an angle of $\pi /6$ between them
3. C
   perpendicular
4. D
   parallel