Consider the helix $\mathbf{r} (t) = \left( \cos( -3 t), \sin( -3 t), 1 t \right)$. Compute, at $t = \frac{\pi}{6}$:

A. The unit tangent vector $\mathbf{T} =$ ( , , )

B. The unit normal vector $\mathbf{N} =$ ( , , )

C. The unit binormal vector $\mathbf{B} =$ ( , , )

D. The curvature $\kappa =$