read this sentence: the speed of light can change depending on the medium through which it passes. which…

read this sentence: the speed of light can change depending on the medium through which it passes. which word means about the same thing as medium? a water b spectrum c substance d radiation
Answer
Brief Explanations:
In the context of light - speed changing, a medium is a substance through which light travels. Water is a specific type of medium, but "substance" is a more general term that encompasses all possible media for light. "Spectrum" refers to the range of wavelengths of electromagnetic radiation. "Radiation" is energy in the form of waves or particles. So "substance" is closest in meaning to "medium" here.
Answer:
C. substance