Give the Amplitude or Period as Requested $y = - 2 \cos \frac { 1 } { 3 } x$

Multiple Choice

Give the amplitude or period as requested.
-Period of $y = - 2 \cos \frac { 1 } { 3 } x$

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