Determine the Exact Value of the Following Expression $$\cos \left( 120 ^ { \circ } - 0 ^ { \circ } \right)$$

Multiple Choice

Determine the exact value of the following expression.
$$\cos \left( 120 ^ { \circ } - 0 ^ { \circ } \right)$$

A) $- \frac { \sqrt { 3 } } { 2 }$
B) $\frac { 1 } { 2 }$
C) $\frac { \sqrt { 3 } } { 2 }$
D) $- \frac { 1 } { 2 }$
E) $\frac { 1 } { 2 } - \frac { \sqrt { 3 } } { 2 }$