Find the Unit Tangent Vector $\mathbf { T } ( t )$

Multiple Choice

Find the unit tangent vector $\mathbf { T } ( t )$ for $\mathbf { r } ( t ) = 2 t \mathbf { i } + 6 t \mathbf { j } + 3 t \mathbf { k }$ at $t = - 1$

A) $- 2 \mathbf { i } - 6 \mathbf { j } - 3 \mathbf { k }$
B) $\frac { 2 } { 7 }$ i + $\frac { 6 } { 7 }$ j + $\frac { 3 } { 7 }$ k
C) $- \frac { 2 } { 49 }$ i $- \frac { 6 } { 49 }$ j $- \frac { 3 } { 49 }$ k
D) $2 \mathbf { i } + 6 \mathbf { j } + 3 \mathbf { k }$