8If the two sound waves produce beats, it is necessary that the two have:

Explanation

Beats occur when two sound waves of similar amplitudes and slightly different frequencies interfere with each other. This interference causes alternating constructive and destructive interference, resulting in the variations in loudness perceived as beats. Option B is correct because the slight difference in frequencies is essential for the creation of this interference pattern. Option A is incorrect because identical frequencies do not result in interference patterns. Option C is incorrect because differences in amplitude do not affect the beat frequency; they only affect the intensity of the sound. Option D is incorrect because the same time periods imply the same frequencies, which do not result in beats.