Let $f ( x ) = \sin x - e ^ { x }$

Multiple Choice

Let $f ( x ) = \sin x - e ^ { x }$ If $x \in [ - \pi , 3 \pi ]$ then ƒ has a horizontal tangent line for each x in

A) 0
B) $\left\{ \frac { \pi } { 2 } \right\}$
C) $\{ \pi \}$
D) $\left\{ \frac { 3 \pi } { 2 } \right\}$
E) $\{ 0,2 \pi \}$