A string is cut into three parts, having fundamental frequencies $n_1$, $n_2$ and $n_3$ respectively. Then original fundamental frequency 'n' related by the expression as :

Question

( A ) $n=\frac{n_1+n_2+n_3}{3}$
( B ) $n=n_1\times n_2\times n_3$
( C ) $\frac{1}{n}=\frac{1}{n_1}+\frac{1}{n_2}+\frac{1}{n_3}$
( D ) $n=n_1+ n_2+n_3$