Write the Expression as the Sine, Cosine, or Tangent of an Angle

Multiple Choice

Write the expression as the sine, cosine, or tangent of an angle.
- $\frac { \tan 5 x - \tan 4 y } { 1 + \tan 5 x \tan 4 y }$

A) $\tan ( 5 x - 4 y )$
B) $\tan \left( \frac { 5 x - 4 y } { 2 } \right)$
C) $\tan \left( \frac { 5 x + 4 y } { 2 } \right)$
D) $\tan ( 5 x + 4 y )$