Which one of the following is a necessary and sufficient condition for
$$\sum _ { k = 1 } ^ { n } \sin \left( \frac { k \pi } { 3 } \right) = \frac { \sqrt { 3 } } { 2 }$$
to be true?
A $n = 1$\\
B $n$ is a multiple of 3\\
C $n$ is a multiple of 6\\
D $n$ is 1 more than a multiple of 3\\
E $n$ is 1 more than a multiple of 6\\
F $n$ is 1 more than a multiple of 6 or $n$ is 2 more than a multiple of 6