Concept:
The load carrying capacity of a pile group is obtained by multiplying the capacity of one pile by the number of piles and the group efficiency.
The formula is
\[
\boxed{
Q_g=\eta \times n \times Q_p
}
\]
where
\[
\eta=\text{Group efficiency},
\]
\[
n=\text{Number of piles},
\]
\[
Q_p=\text{Load carrying capacity of one pile}.
\]
Step 1: Write the given data.
\[
Q_p=200\text{ kN}
\]
\[
n=9
\]
\[
\eta=0.8
\]
Step 2: Calculate the pile group capacity.
\[
Q_g
=
0.8\times9\times200
=
1440\text{ kN}
\]
Hence,
\[
\boxed{Q_g=1440\text{ kN}.}
\]
Therefore, the correct option is
\[
\boxed{(C)\;1440\text{ kN}.}
\]