The frequencies of three tuning forks $A$,$B$,and $C$ are related as $n_{A} > n_{B} > n_{C}$. When the forks $A$ and $B$ are sounded together,the number of beats produced per second is $n_1$. When forks $A$ and $C$ are sounded together,the number of beats produced per second is $n_2$. How many beats are produced per second when forks $B$ and $C$ are sounded together?

• A
  $n_1 - n_2$
• B
  $\frac{n_1 + n_2}{2}$
• C
  $n_2 - n_1$
• D
  $n_1 + n_2$