A sound wave is shown on the screen of a cathode-ray oscilloscope, as illustrated. The time-base setting is $0.50\ \text{ms}$ per division. What is the frequency of the sound wave?
- A$250\ \text{Hz}$
- B$500\ \text{Hz}$
- C$670\ \text{Hz}$
- D$1300\ \text{Hz}$