Let $f ( x ) = x ^ { 4 } - 2 x ^ { 3 } + 1$

Multiple Choice

Let $f ( x ) = x ^ { 4 } - 2 x ^ { 3 } + 1$ The set of all critical numbers of ƒ is

A) $\left\{ 0 , - \frac { 3 } { 2 } \right\}$
B) $\left\{ 0 , \frac { 3 } { 2 } \right\}$
C) $\left\{ 1 , - \frac { 3 } { 2 } \right\}$
D) $\left\{ 1 , \frac { 3 } { 2 } \right\}$
E) $\{ 0,2 \}$