Detailed Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Q: Passage: The variable is the speed of light. For the relationship to hold mathematically, if the speed of light is used in m/s, the wavelength must be in meters and the frequency in Hertz. Answer: hertz
A:
The variable is the speed of light. for the relationship to hold mathematically, if the speed of light is used in m/s, the wavelength must be in meters and the frequency in what?