Let $f ( x ) = x - \sin x$ On $[ 0,2 \pi ]$

Multiple Choice

Let $f ( x ) = x - \sin x$ on $[ 0,2 \pi ]$ The set of all critical numbers of ƒ is

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