For the Given Function, Find the Critical Numbers $y = \frac { x ^ { 4 } } { 4 } - \frac { x ^ { 3 } } { 3 } - 4$

Multiple Choice

For the given function, find the critical numbers. $y = \frac { x ^ { 4 } } { 4 } - \frac { x ^ { 3 } } { 3 } - 4$

A) $x = 0 \text { and } x = 1$
B) $x = 0 \text { and } x = 4$
C) $x = 0 \text { and } x = - 4$
D) $x = 0 \text { and } x = - 1$
E) $x = - 1 \text { and } x = 1$