Task: Question Generation
Input (English): Background Paragraph: Electromagnetic radiation is energy that travels in waves across space as well as through matter. Most of the electromagnetic radiation on Earth comes from the sun. Like other waves, electromagnetic waves are characterized by certain wavelengths and wave frequencies. Wavelength is the distance between two corresponding points on adjacent waves. Wave frequency is the number of waves that pass a fixed point in a given amount of time. Electromagnetic waves with shorter wavelengths have higher frequencies and more energy. 
Story: David is experimenting with electromagnetic waves. He has four different waves to study, wave A, wave B, wave C, and wave D. In wave A, distance between two corresponding points on adjacent waves is greater than that of wave B.
In wave C, the number of waves that pass a fixed point in a given time is greater than that of wave D.
Output (English): Which wave has lower frequency, wave C or wave D?