A microphone is connected to a cathode-ray oscilloscope (CRO). A tuning fork is struck and then placed beside the microphone, producing the waveform shown on the CRO screen. The CRO time-base setting is $2.00\,\text{ms}$ per division. What is the most suitable estimate of the frequency of the sound made by the tuning fork?
- A$63\,\text{Hz}$
- B$170\,\text{Hz}$
- C$250\,\text{Hz}$
- D$500\,\text{Hz}$