Find the Largest Open Intervals Where the Function Is Concave $f(x)=x^{4}-6 x^{3}$

Multiple Choice

Find the largest open intervals where the function is concave upward.
- $f(x) =x^{4}-6 x^{3}$

A) $(0,3)$
B) $(-\infty, 0) ,(3, \infty)$
C) $(-\infty, \infty)$
D) $(-\infty, 0)$