The Function Graphed Is of the Form $$y = \cos x + c , y = \sin x + c , y = \cos ( x - d ) , \text { or } y = \sin ( x - d )$$

The function graphed is of the form $$y = \cos x + c , y = \sin x + c , y = \cos ( x - d ) , \text { or } y = \sin ( x - d )$$ where d is the least possible
positive value. Determine the equation of the graph.
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A) $\cos x - \frac { \pi } { 6 }$
B) $\sin \left( x - \frac { \pi } { 6 } \right)$
C) $\cos \left( x - \frac { \pi } { 6 } \right)$
D) $\cos \left( x - \frac { \pi } { 3 } \right)$