Let $f$ be the function defined on $] 0 ; + \infty \left[ \text{ by } f ( x ) = x ^ { 2 } \ln x \right.$.
A primitive $F$ of $f$ on $] 0$; $+ \infty [$ is defined by:\\
a. $F ( x ) = \frac { 1 } { 3 } x ^ { 3 } \left( \ln x - \frac { 1 } { 3 } \right)$;\\
b. $F ( x ) = \frac { 1 } { 3 } x ^ { 3 } ( \ln x - 1 )$;\\
c. $F ( x ) = \frac { 1 } { 3 } x ^ { 2 }$;\\
d. $F ( x ) = \frac { 1 } { 3 } x ^ { 2 } ( \ln x - 1 )$.