The two functions $F ( n )$ and $G ( n )$ are defined as follows for positive integers $n$ :
$$\begin{aligned}
& F ( n ) = \frac { 1 } { n } \int _ { 0 } ^ { n } ( n - x ) d x \\
& G ( n ) = \sum _ { r = 1 } ^ { n } F ( r )
\end{aligned}$$
What is the smallest positive integer $n$ such that $G ( n ) > 150$ ?
A 22
B 23
C 24
D 25
E 26