Final answer:
To match the frequency of the top and bottom waves, one must either increase the frequency of the bottom waves (by decreasing their wavelength) or decrease the frequency of the top waves (by increasing their wavelength).
Step-by-step explanation:
In addressing the question about wave frequencies, let's first consider the relationship between the frequency and wavelength of a wave, as they are inversely related. According to the information provided, when the period of a wave increases, its frequency decreases. Therefore, if the bottom waves have a higher wavelength (lower frequency) than the top waves, to match the top waves' frequency, one would have to increase the frequency of the bottom waves, which can be done by decreasing their wavelength. Alternatively, to match the bottom waves' frequency, the top waves' frequency must be decreased by increasing their wavelength.
Based on this understanding of wave properties, the correct statement about how to match the frequencies of the two waves is that decreasing the frequency of the top waves by half will cause it to match the bottom waves (Option C). If the top waves' frequency is reduced by half, their wavelength would double, meaning the frequency would be the same as that of the bottom waves if they started with double the wavelength or half the frequency of the top waves to begin with.