D. 5 m/s
This is because the formula to find the speed of a wave is the wavelength divided by the period (wavelength/period). Since the wavelength is 100 m and the period is 20 s, the speed is 5 m/s.
If you are confused on the units, then think about it this way: If you put this problem in fraction form, it would be: 100 m/20 s. 100 divided by 20 is 5, but m and s are still there. Remember that this "/" is also a division symbol. Therefore, the unit will be m/s
I would go with the third option because it seems logical. He had a big imagination and was very creative. Hope I helped
Secondary wave is the answer
