A cathode-ray oscilloscope (c.r.o.) is connected to an alternating voltage, and the screen shows the trace below. The oscilloscope time-base setting is $0.5\,\text{ms cm}^{-1}$ and the Y-plate sensitivity is $2\,\text{V cm}^{-1}$. Which statement about the alternating voltage is correct?
- AThe amplitude is $3.5\,\text{cm}$.
- BThe frequency is $0.5\,\text{kHz}$.
- CThe period is $1\,\text{ms}$.
- DThe wavelength is $4\,\text{cm}$.