Select the correct answer. Natasha holds the two ends of a string in her hands and then moves her hands up and down so that a wave travels from one end of the string to the other end. In which case will she have a standing wave along the string? A. The resultant wave rises and falls in amplitude over time and has a frequency equal to that of the waves. B. The resultant wave has a fixed amplitude and a frequency twice that of the waves. C. The resultant wave has a fixed amplitude and a frequency equal to that of the waves. D. The resultant wave rises and falls in amplitude over time and has a frequency twice that of the waves