The circle with a radius of one unit is partitioned into twelve equal arcs, where each arc corresponds to specific t-values. Determine the value of the trigonometric function at the given real number t using the (x,y) coordinates in the diagram or specify that the expression is undefined.

$\sec(\frac{5\pi}{3})$

• A. $\frac{2\sqrt3}{3}$
• B. $-\frac{2\sqrt3}{3}$
• C. $2$
• D. $\frac12$