Find the Right Side of the Identity $\frac { \sin s + \sin t } { \sin s + \sin t } = ?$

Multiple Choice

Find the right side of the identity. $\frac { \sin s + \sin t } { \sin s + \sin t } = ?$

A) $\tan \left( \frac { s + t } { 2 } \right)$
B) $\tan ( s - t )$
C) $\sin ( s + t )$
D) $$\cot \left( \frac { s + t } { 2 } \right)$$
E) $\tan \left( \frac { s - t } { 2 } \right)$