Evaluate the Expression $\tan \frac { a } { 2 }$

Multiple Choice

Evaluate the expression. $\tan \frac { a } { 2 }$

A) $\cos a + \cot a$
B) $\cos a - \cot a$
C) $\csc a - \cot a$
D) $\csc a - \tan a$
E) $\csc a + \cot a$