The graph shows how the intensity $I$ varies with distance $x$ in a stationary sound wave in air. The speed of sound in air is $340\,\text{m s}^{-1}$. What is the frequency of the sound wave?
- A$1700\,\text{Hz}$
- B$2300\,\text{Hz}$
- C$3400\,\text{Hz}$
- D$6800\,\text{Hz}$