Find the Specified Quantity $y = 2 \cos \left( \frac { 1 } { 3 } x + \frac { \pi } { 3 } \right)$

Multiple Choice

Find the specified quantity.
-Find the period of $y = 2 \cos \left( \frac { 1 } { 3 } x + \frac { \pi } { 3 } \right)$

A) $6 \pi$
B) $3 \pi$
C) $\frac { 2 \pi } { 3 }$
D) $2 \pi$