Whilst it is hard to read the graph because there are no labelled markers on the time axis and the ‘5.0’ and ‘10.0’ are in such big lettering (to me it actually looks closer to 4 cycles in 10 milliseconds), nevertheless, only option A is anywhere close in magnitude to the correct frequency. Frequency (Hz) is defined as the the number of cycles in a second, so each cycle is roughly 2.0 to 2.5 milliseconds, so somewhere between 400 to 500 Hz for which only option A fits.