High energy waves have
choose one answer.
a. long wavelengths and low frequencies.
b. long wavelengths and high frequencies.
c. short wavelengths and low frequencies.
d. short wavelengths and high frequencies

Wavelength and frequency are inversely related, and frequency and energy are directly related. This means that if the wavelength increases, both frequency and energy are going to decrease (since they direction is the same), and vice versa.
So, having that in mind, high energy waves have D. short wavelengths and high frequencies. 

50 meters per 5 seconds

Independent variable is something that is changed in a experiment.