Find the Exact Value of the Function $\frac { 2 \sqrt { 3 } } { 3 }$

Multiple Choice

Find the exact value of the function. Rationalize the denominator if necessary.
-sec 240°

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