Answer the Question $y = 2 \cos \left( \frac { 1 } { 3 } x \right)$

Multiple Choice

Answer the question.
-Which one of the equations below matches the graph?

A) $y = 2 \cos \left( \frac { 1 } { 3 } x \right)$
B) $y = 2 \sin \left( \frac { 1 } { 3 } x \right)$
C) $y = 2 \cos ( 3 x )$
D) $y = - 2 \sin \left( \frac { 1 } { 3 } x \right)$