Space Find the Acceleration $\mathbf { a } ( t )$

Multiple Choice

$\text { The position vector } \mathbf { r } ( t ) = 4 t \mathbf { i } + 2 t \mathbf { j } + \frac { 1 } { 6 } t ^ { 2 } \mathbf { k } \text { describes the path of an object moving in }$ space. Find the acceleration $\mathbf { a } ( t )$ of the object.

A) $\mathbf { a } ( t ) = \frac { 1 } { 6 } \mathbf { k }$
B) $\mathbf { a } ( t ) = 4 \mathbf { i } + 2 \mathbf { j }$
C) $\mathbf { a } ( t ) = 4 \mathbf { i } + 2 \mathbf { j } + \frac { 1 } { 3 } \mathbf { k }$
D) $\mathbf { a } ( t ) = 4 \mathbf { i } + 2 \mathbf { j } + 2 \mathbf { k }$
E) $\mathbf { a } ( t ) = \frac { 1 } { 3 } \mathbf { k }$